Manual for the Sealevel Talos API Framework in PDF Format. This manual includes the Talos API documentation for Windows CE 6.0 supporting the R9 family of embedded RISC computers.

Manual for Sealevel SeaMAX Software in PDF Format. This manual includes the SeaMAX API documentation with support for SeaI/O, SeaDAC and SeaDAC Lite modules.

The ACC-188 USB synchronous serial radio adapter (Item# 9065) and free software from DISA enables tactical radios with the capability to transmit and receive IP data such as email, text messages, GPS maps, images, coordinates, and other communications. The system is nonproprietary and MIL-STD-188-184 compliant, allowing for interoperability with various radios without multiple connections or additional equipment.

Learn how warfighters can benefit greatly from having fully interoperable radio IP-based data communications at the theater level in our "USB to Synchronous Cable Enables IP Data Communications for Tactical Radios" White Paper. Download the PDF file below.

Article by Earle Foster
(Reprinted from Defense Tech Briefs, February 2010)

The ACC-188 USB synchronous serial radio adapter (Item# 9065) and free software from DISA enables tactical radios with the capability to transmit and receive IP data such as email, text messages, GPS maps, images, coordinates, and other communications. The system is nonproprietary and MIL-STD-188-184 compliant, allowing for interoperability with various radios without multiple connections or additional equipment.

Learn how warfighters can benefit greatly from having fully interoperable radio IP-based data communications at the theater level in our "USB to Synchronous Cable Enables IP Data Communications for Tactical Radios" White Paper. Download the PDF file below.

Sealevel SeaI/O devices offer flexible I/O expansion to APC Netbotz remote environmental monitoring equipment. All APC NetBotz appliances that have a USB port support SeaI/O 450U and 462U modules to expand the amount of digital I/O. SeaI/O 450U modules provide 16 Form C relay outputs useful for locking doors, turning lights on or off, and other relay controlled actions. SeaI/O 462U modules provide 96 channels of TTL digital I/O useful for monitoring a large number of dry contact sensors. APC has developed a useful application note (download link below) with more information on using SeaI/O modules with your APC NetBotz appliance.

On February 16, 2010, Kontron customers received an End of Life (EOL) notification (PDF link at bottom of article) regarding the elimination of serial and I/O devices from their product listing. For more than 20 years, Sealevel has manufactured these products for Kontron. Sealevel will continue to offer these serial and I/O devices following Kontron’s Last Time Buy on August 31, 2010. 

Below you will find a reference table showing the Kontron product and corresponding Sealevel product. The Sealevel products listed on this page are the same products you purchased from Kontron. From sales to technical support, our team will ensure that you purchase the correct product for your application. 

For Sales Support Contact:
James Priest
Channel Sales Manager
james.priest@sealevel.com
+1 864-843-4343

Charlie McKenzie
Channel Sales
charlie.mckenzie@sealevel.com
+1 864-843-4343

For Technical Support Contact:
support@sealevel.com
+1 864-843-4343

Kontron to Sealevel Part Number Cross Reference

Serial I/O - Asynchronous
Kontron Part#	Description	Sealevel Part#
USB
USB-ULTRA485	USB to 1 Port RS-422/485	2102
USB-COM232I	USB to 1 Port RS-232 (Isolated)	2103
USB-ULTRA485I	USB to 1 Port RS-422/485 (Isolated)	2104
USBCOMM232/2	USB to 2 Port RS-232	2201
USB-UC422/2	USB to 2 Port RS-422/485	2202
USB-UC232/2	USB to 2 Port RS-232/422/485	2203
USB-COMM232/4	USB to 4 Port RS-232	2401
USB-UC422/4	USB to 4 Port RS-422/485	2402
USB-UC232/4	USB to 4 Port RS-232/422/485	2403
USB-COMM232/8	USB to 8 Port RS-232	2801
USB-UC422/8	USB to 8 Port RS-422/485	2802
USB-UC232/8	USB to 8 Port RS-232/422/485	2803
PCI
ULTRA485	PCI to 1 Port RS-422/485	7105
COMM232PCI/2-55	PCI to 2 Port RS-232	7202
COMM232PCI/2-85	PCI to 2 Port RS-232 (16C850 UARTs)	7202-SE
UC232PCI/2-851	PCI to 2 Port RS-232/422/485	7203
UC422PCI/4-55	PCI to 4 Port RS-422/485	7402
UC422PCI/4-85	PCI to 4 Port RS-422/485 (16C850 UARTs)	7402-SE
UC232PCI/4-85	PCI to 4 Port RS-232/422/485	7404
Low Profile PCI
COMM+850	Low Profile PCI to 1 Port RS-232	7104
UPCI-COMM4/EX-555-LP	Low Profile PCI to 4 Port RS-232 (DB25)	7406
UPCI-COMM4/EX-559-LP	Low Profile PCI to 4 Port RS-232 (DB9)	7406-DB9
CompactPCI
CPCI-UC232/2	cPCI 2 Port RS-232/422/485	7901
CP6-3UADAPTER	cPCI 3U to 6U Adapter	7902
CPCI-UC232/2I	cPCI 2 Port Isolated RS-232/422/485	7903
CPCI-UC232/4	cPCI 4 Port RS-232/422/485	7904
CPCI-WINCOMM8	cPCI 8 Port RS-232 (DB25)	7905
CPCI-WINCOMM8-DB9	cPCI 8 Port RS-232 (DB9)	7905-DB9 (Call)
PC/104
SP104/232	PC/104 1 PORT RS-232	3551
ISA
ULTRA-485	ISA 1 Port RS-422/485	3055
SPRT2B/AT	ISA 2 Port RS-232/422/485	3087
DUAL232/AT	ISA 2 Port RS-232	3088
ULTRA-485/2ISO	ISA 2 Port Isolated RS-422/485	3189
WINCOMM8/C	ISA 8 Port RS-232 (DB25)	3420
HS-RS232/DP-85	ISA 2 Port High Speed RS-232 (16C850 UART)	3188-SE (Call)
Serial I/O - Synchronous
Kontron Part#	Description	Sealevel Part#
PCI-ACB	PCI 1 Port RS-232/422/485/449/V.35 (Z85230)	5102
PC-ACB-MP	PCMCIA 1 Port RS-232/422/485/530/530A/V.35 (Z85233)	3612
ACB-104/B	PC/104 1 Port RS-232/422/485/449/V.35 (Z85230)	3512
Digital I/O
Kontron Part#	Description	Sealevel Part#
USB
USB-DIO16	USB 8 Isolated Input /8 Reed Relay Output	8209
USB-16REL	USB 16 Reed Relay Output	8208
USB16ISO	USB 16 Isolated Inputs	8207
USB-DIO8	USB 8 Isolated Input/8 Form C Output	8206
USB-DIO96	USB 96 Channel Digital I/O	8205
USB-DIO48	USB 48 Channel Digital I/O	8203
PCI
PCI-16REL	PCI 16 Relay Output Digital I/O Card	8003
PCI-DIO32	PCI 16 Isolated Inputs / 16 Reed Relay Outputs	8004
PCI-DIO32-24-S	PCI 16 Isolated Inputs / 16 Reed Relay Outputs (For 24V with 2.2k resistors)	8004-2000 (Call)
PCI-16ISO	PCI 16 Isolated Inputs	8006
PCI-32REL	PCI 32 Reed Relay Outputs (Standard Male/Male Cable)	8007
PCI-32REL-B	PCI 32 Reed Relay Outputs (With CA-173 A Side/B Side Cable)	8007-A01 (Call)
ISA
DIO-32B	ISA 16 Isolated Inputs / 16 Reed Relay Outputs	3093
DIO-32B-24V	ISA 16 Isolated Inputs / 16 Reed Relay Outputs (For 24V)	3093-104 (Call)
16ISO	ISA 16 Isolated Inputs	3094
16ISO Special Order	ISA 16 Isolated Inputs (With 761-3-R2.2K)	3094-104 (Call)
16REL	ISA 16 Reed Relay Outputs	3095
DIO-16	ISA 8 Isolated Inputs / 8 Reed Relay Outputs	3096
32REL-B	ISA 32 Switched Relay Outputs	3098
Custom Counter/Timer Boards
Kontron Part#	Description	Sealevel Part#
PCI/DCC5-P10433-01A	PCI 16-bit 5-Channel Counter/Timer Board (PCIDCC5-P)	9004 (Call)
PCI/DCC10-P10433-02A	PCI 16-bit 10-Channel Counter/Timer Board (PCIDCC10-P)	9005 (Call)
PCI/DCC20-P10433-03A	PCI 16-bit 20-Channel Counter/Timer Board (PCIDCC20-P)	9006 (Call)

The USB Digital I/O QuickStart Guide in PDF format.

For guidance covering the initial steps of compiling and running individual example projects using Microsoft Visual Studio, please refer to the SeaMAX API Documentation.

To access the documentation from the Start Menu, click All Programs and locate the Sealevel SeaMAX folder. In the SeaMAX folder, click on Documentation, and then click on the SeaMAX API Documentation link, which will open in your default browser.

Click on "Example Code & Instructions" under the Getting Started heading. Be sure to also read the "Integrating SeaMAX into Your Project" for a complete list of integration steps.

The SeaMAX Software package automatically installs several application samples with source code in the Example Projects sub-folder.

To access the samples from the Start Menu, click All Programs and locate the Sealevel SeaMAX folder. In the SeaMAX folder, click on Documentation, and then click on the Example Projects Folder shortcut. Select your development platform from the available choices.

The sample applications are designed to let you walk through the same integration steps that are required to integrate SeaMAX with your own project.

A Quadrature counter, also known as a Quadrature decoder, shaft decoder, or rotary decoder, is a type of digital input that uses a two-bit Gray code input to increase or decrease a value. The Quadrature counter works in combination with an optical or mechanical encoder, also known as a rotary or shaft encoder, to monitor the exact position, speed, and direction of a DC motor shaft.

The Quadrature counter works by reading the angular position of a shaft and converting it to high resolution digital data. This data is used for synchronizing moving parts for reliable, trouble-free operation. Optical encoders are commonly found in motors installed in industrial control applications, precision robotics, drive shafts, and rotating radar platforms.

Sealevel includes Quadrature counters in certain models of our R9 family of embedded RISC computers.

This Quick Start Guide is excerpted from the SBC-R9 hardware manual. For a complete overview of the hardware, including technical descriptions, connector diagrams, pin outs and debugging information, please refer to the product manual. If you want to get started right away, you may jump to the section Quick Start section below.

Before You Get Started

What's Included
The SBC-R9 is shipped with the following items. If any of these items are missing or damaged, please contact Sealevel for replacement.

• SBC-R9 ARM9 Embedded RISC Single Board Computer
• SD Card with CE runtime image, Talos .NET Framework, application samples, and documentation
• CD with Setup files and documentation
• Microsoft® Windows® CE 6.0 Core license

QuickStart Kit
The SBC-R9 QuickStart Kit (Item# SBC-R9-KT) is available, which includes the most common accessories. For applications with specialized hardware requirements, developers can use the SBC-R9 as a platform for application development while Sealevel designs a customized target system specific to the user’s application requirements.

The SBC-R9-KT includes the following items:

• SBC-R9 ARM9 Embedded RISC Single Board Computer
• SD Card with CE runtime image, Talos .NET Framework, application samples, and documentation
• CD with setup files and documentation
• Microsoft Windows CE 6.0 Core License
• TR134 – 100-240VAC to 12VDC @ 2.5A, wall mount power supply
• CA179 – USB Type A to USB Type B, device cable
• CA429 – R9 serial debug cable
• CA246 – CAT5 patch cable, 6' length
• CA273 – 40-pin IDC ribbon cable to (4) DB9M connectors

SBC-R9 Quick Start

Remove the contents from the box.

Insert the accompanying CD into your PC and run the installation program. This will install Talos Framework binaries, documentation, and examples on your PC. (See Figure 1)

Figure 1. Installation Wizard

After installation, the package can be found in Windows by clicking Start > All Programs > Sealevel Systems > R9 Development.

Verify that the accompanying SDCARD (located on the bottom card slot B (J11) of the SBC-R9) is correctly inserted. The contents of the SDCARD will allow the SBC-R9 to run Windows CE 6.0 OS when power is applied to the board.

Warning! To avoid accidental damage, be sure to follow proper ESD procedures by grounding yourself and the board.

Apply power to the SBC-R9 by connecting the TR134 Molex connector to the SBC-R9 (P3) connector. Attach the other end of the TR134 into a 120VAC wall outlet. (See Figure 2.)

Figure 2.  Connect the TR134 Molex connector to the SBC-R9 (P3) connector

Use a standard USB device cable and connect the Type B connector to the SBC-R9. (See Figure 3.) Connect Type A connector into the host PC.

Figure 3. Connect the Type B connector to the SBC-R9

You are now ready to set up a USB communication interface between the host PC and the SBC-R9 board. Depending on which operating system you are using – Windows Vista or XP – the setup experience will vary.

Windows Device Center

If your host PC is running Windows Vista or later and you are connected to the internet, then Windows Mobile Device Center software will install automatically. If you are not connected to the internet but have obtained the Mobile Device Center software manually then running their setup will achieve the same result.

After installation, a negotiation will begin between the PC and the SBC-R9 board and the device center connection screen will appear. (See Figure 4.)

Figure 4. Device Center connected screen

Using your mouse, select "Connect without setting up your device". The idea is to explore the file system on the SBC-R9 without setting up synchronization with contacts, calendar, or e-mail. Now choose "File Management > Browse the contents of your device" from the screen. (See Figure 5.)

Figure 5. Device Center File Management

This action opens a standard Windows Explorer where the default file contents of the SBC-R9 can be read or written to. (See Figure 6.)

Figure 6. Contents of SBC-R9

Windows ActiveSync for XP

If your host PC is running Windows XP, ActiveSync is required to establish connection to the SBC-R9. ActiveSync differs from Mobile Device Center in that having an internet connection will not establish an automatic download and installation. For installation procedures, refer to Microsoft's website. After installation, a negotiation will begin between the PC and the SBC-R9 board, and the "New Partnership" dialog will appear. (See Figure 7.)

Figure 7. ActiveSync New Partnership screen

Using your mouse, select "No" and then select "Next". The ActiveSync main dialog will appear. Select the "Explore" icon. This action opens a standard Windows Explorer where the default file contents of the SBC-R9 can be read or written. (See Figure 8.)

Figure 8. ActiveSync Main Dialog screen

You are now ready to set up a complete development environment for building and debugging smart device applications and libraries. The next section guides you by example using Microsoft Visual Studio.

Programming using the .NET Compact Framework

Application Development

Introduction
With .NET Compact Framework coupled with our Talos .NET Framework, C# and VB.NET programmers can develop powerful embedded applications on the SBC-R9 such as mobile, robotics, home automation, industrial, and a broad range of other embedded applications. The low cost of licensing for Windows 6.0 CE has created an ideal environment to develop a new generation of embedded products around the SBC-R9.

Our Talos Framework allows access to the more specific I/O sections of the SBC-R9 development board such as analog and digital I/O points, CAN bus, quadrature counter inputs, and the multi-electrical interface serial ports. A complete list of the API documentation can be found either in Windows by clicking Start > All Programs > Sealevel Systems > R9 Development > Talos Documentation.html or by referencing the Sealevel website.

Writing .NET applications for the SBC-R9 is very similar to writing desktop or console applications for XP and Vista. The only difference is the amount of resources available. Because the memory footprint is smaller compared to a desktop computer, care should be taken where allocation of memory is concerned, such as huge object creations.

Requirements

• Visual Studio 2005 or 2008
• .NET Compact Framework 3.5

Getting Started
For this demonstration, we will construct a smart device console application using Visual C#. Start Visual Studio and select File > New > Project. A 'New Project' dialog will appear. Select a project type of Visual C# > Smart Device. Select 'Smart Device Project' as the Template. Make sure the combo box has .NET Framework 3.5 selected. Type the name of the project. In this case, call it AnalogIO. (See Figure 9.)

Figure 9. Visual Studio New Project dialog

Click the "OK" button. The next configuration screen allows you to select the type of project you are creating. Select "Windows CE" for the target platform, .NET Compact Framework version 3.5 and select the "Console Application" icon for the template. (See Figure 10.)

Figure 10. Visual Studio Add Smart Device dialog

Once you have selected all of the configuration options, click the "OK" button. You will now see a console application template called AnalogIO in Visual Studio. (See Figure 11.)

Figure 11. Visual Studio Main Window

We can now add the references to the Talos Framework. Right click on the "References" and select the "Add Reference…" selection. (See Figure 12.)

Figure 12. Adding References to Project

An 'Add Reference' dialog will appear. Click on the 'Browse' tab then search for the installed library path "C:\Program Files\Sealevel Systems\R9 Development\Assemblies". If you don't see a list of the R9 libraries as shown in Figure 12, then refer to the SBC-R9 QuickStart section for software installation details. While holding down the CTRL key, click on both "SLCorLib.dll" and "Talos.dll". Click the "OK" button. (See Figure 13.)

Figure 13. Core library reference

Both DLLs should appear in your "References" list. (See Figure 14.)

Figure 14. Verification of added library references

Now that the Talos Framework has been referenced, you have access to all the I/O points exposed on the SBC-R9 device.

Replace the contents of the "AnalogIO" class file created by the project wizard with the installed AnalogI/O C# example. This example can be found at "C:\Program Files\Sealevel Systems\R9 Development\Samples\C#\AnalogIO\AnalogIO\Program.cs".

From Visual Studio's menu bar, select "Build > Build AnalogIO". After the build process has completed select from the same menu bar, "Build > Deploy AnalogIO". A "Deploy AnalogIO" dialog will appear for you to choose the appropriate target. Choose "Windows CE Device" then press the 'Deploy' button. (See Figure 15.)

Figure 15. Choose Windows CE Device and Deploy

After the deployment phase a console will appear to display the current count of analog points and their associated current values.

More examples can be found from the installation directory or the supplied SDCARD under "..\R9 Development\Sample\C#" and "..\R9 Development\Sample\VB.NET".

This Quick Start Guide is excerpted from the SBC-R9 hardware manual. For a complete overview of the hardware, including technical descriptions, connector diagrams, pin outs and debugging information, please refer to the product manual.

WinSSD currently only provides support for the 511-bit pattern defined in ITU document O.153 paragraph 2.1. This test pattern is common to many BERT applications. If you need other algorithms, contact Sealevel technical support for assistance.

Sealevel recommends using the installed COM numbers if at all possible to avoid system conflicts. If you previously installed a USB or PCMCIA serial interface, it will have resources assigned by the operating system. If the device is not currently connected to your computer, these COM assignments will not be apparent and forcing new COM port assignments will create a conflict when the devices are reconnected at a later time.

One scenario where you would have to change the COM port assignments is when your legacy application only works at COM1 through COM4 and the Sealevel serial device you installed comes in at COM5 or higher. Another scenario might occur when you install a multiport serial card and the COM port numbers are not assigned consecutively and you want them to appear consecutive.

In Windows 7, Vista, XP, or 2000, you can change the COM port assignments in Device Manager. In Windows 95, 98, ME, or NT, you’ll need to use Sealevel’s Port Manager or Advanced Ports utility.

Sealevel recommends using the installed COM numbers if at all possible to avoid system conflicts. If you previously installed a USB or PCMCIA serial interface, it will have resources assigned by the operating system. If the device is not currently connected to your computer, these COM assignments will not be apparent and forcing new COM port assignments will create a conflict when the devices are reconnected at a later time.

One scenario where you would have to change the COM port assignments is when your legacy application only works at COM1 through COM4 and the Sealevel serial device you installed comes in at COM5 or higher. Another scenario might occur when you install a multiport serial card and the COM port numbers are not assigned consecutively and you want them to appear consecutive.

Windows 95, 98, ME, and NT did not provide a way to change COM port assignments in Device Manager. Sealevel developed the Port Manager utility (Advanced Ports in NT) to address this Windows limitation. Port Manager is automatically installed when you install the SeaCOM serial driver. In Windows NT, the SeaCOM software driver installs the Sealevel Advanced Ports utility in the Control Panel.

To change COM port assignments using Port Manager in Windows 95, 98, or ME operating systems, follow these steps:

1) Click Start -> All Programs -> SeaCOM -> Port Manager

2) In the Port Manager window, select your current Device in the table by clicking on it to highlight

3) Change the COM port assignment by choosing an available COM number in the Port Name drop box

4) Click on the Apply button, and then the OK button to confirm changes

5) Verify your changes in Device Manager under the Ports (COM & LPT) listing

To change COM port assignments using Advanced Ports in Windows NT, follow these steps:

1) Click Start -> Control Panel
2) In the Control Panel window, double-click the Advanced Ports icon
2) In the Advanced Ports window, select your current Device in the table by clicking on it to highlight
3) Change the COM port assignment by choosing an available COM number in the Port Name drop box
4) Click on the Apply button, and then the OK button to confirm changes
5) Verify your changes in Device Manager under the Ports (COM & LPT) listing

Contact our technical support department if you are still experiencing problems with serial COM port assignments.

Sealevel recommends using the installed COM numbers if at all possible to avoid system conflicts. If you previously installed a USB or PCMCIA serial interface, it will have resources assigned by the operating system. If the device is not currently connected to your computer, these COM assignments will not be apparent and forcing new COM port assignments will create a conflict when the devices are reconnected at a later time.

One scenario where you would have to change the COM port assignments is when your legacy application only works at COM1 through COM4 and the Sealevel serial device you installed comes in at COM5 or higher. Another scenario might occur when you install a multiport serial card and the COM port numbers are not assigned consecutively and you want them to appear consecutive.

In Windows 7, Vista, XP or 2000 operating systems, you can change the COM number assignment using Windows Device Manager.  To change the COM port assignments in Device Manager, follow these basic steps:

1) Click the Start button

2) Right-click on My Computer

3) In the fly-out menu, click Manage

4) In the Computer Management Window, click on Device Manager

5) In the right-hand pane, expand the Ports (COM & LPT) listing by clicking the "+" symbol

6) Right-click on the COM number you want to change and select Properties from the fly-out menu

7) In the Communications Port Properties window, click the Port Settings tab and then click the Advanced button

8) In the Advanced Settings window, you can select the new COM port number from the drop box (be careful not to select a COM number already in use).

9) Click the OK button to confirm your changes. If Windows detects a conflict, choose another COM port number.

10) Click the OK button to close the Communications Port Properties window.

11) The Device Manager window will refresh and the COM assignment will update to reflect your changes

Contact our technical support department if you are still experiencing problems with serial COM port assignments.

Sealevel SeaI/O and SeaDAC devices are fully compatible with other Modbus compliant devices, PLCs and applications.  Many third party software applications and PLCs support interfacing digital I/O devices via the Modbus protocol. Sealevel devices with USB, RS-232, or RS-485 interfaces use the Modbus RTU protocol.  Sealevel devices with Ethernet or Wireless interfaces use the Modbus TCP protocol. Detailed information is included in the documentation installed with the Sealevel SeaMAX software.

Modbus information is available at www.modbus.org.

Depending on your application, Sealevel digital I/O products with either optically isolated inputs or TTL level signaling can be used.

Sealevel products with TTL inputs require tight coupling and will work for simple applications where there is a short distance between the input and output modules. TTL signals require voltages of 5 VDC.

Sealevel digital I/O devices with optically isolated inputs offer increased flexibly over TTL level inputs. The optically isolated inputs can interface over greater distances than possible with TTL signals. Optically isolated inputs are compatible with higher voltages (typically 5-30 VDC) and offer protection from ground loops. Each optically isolated input has an inline current limiting resistor and is non-polarized, so they can be wired without regard to the polarity.

Many third-party software packages (and PLCs) include support for the open and well-documented Modbus protocol. Sealevel SeaI/O modules use the Modbus protocol for communication and control. SeaI/O modules with USB, RS-232, or RS-485 interfaces use the Modbus RTU protocol. Ethernet and wireless SeaI/O modules use the Modbus TCP protocol. More information is included in Sealevel SeaMAX library documentation.

The Modbus protocol is documented at www.modbus.org.

SBC-R9 user manual in PDF format.

SeaIO is the classic software driver that supports our PCI Express, PCI, PC/104, ISA, and classic USB digital I/O devices. SeaMAX is the driver for our latest digital I/O data acquisition products, including SeaI/O modules, SeaDAC modules, and SeaDAC Lite modules.

Most of our bus based adapters, including PCI Express, PCI, PCMCIA, PC/104 and ISA, can be used. The adapter must have a 16C950 UART installed and support the Ring Indicator (RI) signal. The 16C950 UART is necessary to allow the SeaCOM driver to put the adapter into isochronous mode. Ring Indicator accepts the external clock signal which is required to operate in isochronous mode.

Order the serial adapter with an “-SN” suffix, which designates the 16C950 UART. Refer to the pin out diagram of the appropriate product manual for the presence of the Ring Indicator signal.

The HUB7i QuickStart Guide in PDF format.

The HUB7M QuickStart Guide in PDF format.

The HUB7P QuickStart Guide in PDF format.

The SeaI/O 463 Ribbon Cable QuickStart Guide in PDF format.

The TB34 DB9-to-5 Screw Terminal Block Adapter datasheet in PDF format.

The R5220 Relio Industrial Computer datasheet in PDF format.

The Relio R9 RISC Embedded Computing datasheet in PDF format.

The SBC-R9 RISC Embedded Computing datasheet in PDF format.

The 2009 R9 Embedded I/O Server product mailer in PDF format.

The ACC-188 (9065) Synchronous Serial Radio Adapters for Tactical Radio Communications product brochure in PDF format.

Click on the link to view the product pages for the Synchronous Serial Radio Adapters for USB and PCMCIA interfaces.

The eI/O Embedded I/O Modules product brochure in PDF format.

The Relio™ Embedded I/O Servers product brochure in PDF format.

The SeaPAC Flat Panel Solutions product brochure in PDF format.

SeaI/O Data Acquisition Solutions product brochure in PDF format.

The 2006 Sealevel product catalog in PDF format.

This is located in the API Documentation directory when the R9 Development suite is installed. From the Start menu, locate the Sealevel R9 Development folder and choose the Talos API Documentation. You may browse available classes and their members by namespace. These pages will explain the usage and API references that fully document the Talos API, including samples and descriptions of all calls.

You can download the Talos Framework manual in PDF format at the link below.

To simplify installation and configuration, a printed copy of the SeaLINK QuickStart Guide is included with all Ethernet serial server orders.

The 'Set Configuration' and 'Save Configuration' buttons are only available in the synchronous version of WinSSD test utility that is included in the SeaMAC software suite.

Clicking the 'Set Configuration' button will send the configuration currently defined in this window to the SeaMAC driver. If successful, it will cause the driver to be configured as defined. The configuration settings will revert to the previous default settings when you close WinSSD.

Clicking the 'Save Configuration' will send the configuration currently defined in this window to the SeaMAC driver (same as the 'Set Configuration' button). If successful, it will also tell the driver to save the current settings as the new default configuration. The new settings will be available whenever the port is opened, even after a reboot.

This is located in the API Documentation file when SeaMAX is installed. From the Start menu, locate the Sealevel SeaMAX folder and choose Documentation and then SeaMAX API Documentation. For Function call descriptions and examples, select the link titled SeaMAX API. This will explain the Usage and API references that fully document the SeaMAX API, including function calls and enumerations.

You can download the SeaMAX manual in PDF format at the link below.

WinSSD uses the 511-bit [(2^9)-1] pattern defined in the ITU document O.153 section 2.1. This pattern is one bit short of being 64-bytes long. The first bit of the second iteration of the pattern begins as the last missing bit of the previous pattern. The pattern "wraps" around shifted by one bit each time it is sent. A buffer of 511-bytes will hold exactly eight copies of the 511-bit pattern, which is what the Sealevel WinSSD utility is programmed to send and receive. A copy of this pattern is included in the text file below.

BERT stands for Bit Error Rate Test. A BERT test provides information regarding the line quality of a serial communications link. A BERT test is included in the Sealevel WinSSD utility.

Sealevel’s commitment to total customer satisfaction is reflected in the company’s management system achieving ISO 9001:2000 registration in 2002, providing one of the strongest assurances of product/service quality available. In 2009, we achieved ISO 9001:2008 registration, which ensures that the proper processes and business practices are in place to satisfy quality requirements and satisfaction in supplier-customer relationships. Sealevel is audited by Quality Management Institute (QMI), North America’s largest management system registrar.

Download a copy of the Sealevel ISO 9001:2008 certificate in PDF format below.

Sealevel Online Privacy Policy
Sealevel Systems Inc. respects your privacy. We will only collect, store and use your personal information to enhance our business relationship with you and make the use of our products and services easier and more efficient. The personal information we collect is used to process your on-line purchases, provide customer service and support, and share product, service and company news and offerings with you. We do not sell your personal information. Our goal is to ensure the highest levels of security and confidentiality.

How Is Your Information Protected?
Your transmission of technical or financial information to us is secured through encryption. Likewise, all order forms or requests for quotes submitted through the Site, and billing information and account status information accessible through the Site, are secured via encryption.

While we strive to protect your personal or company information by encryption and other means, we cannot guarantee or warrant the security of the information you transmit to us, and if you choose to use our Site, you do so at your own risk.

Cookies
A cookie is an element of data that a website can send to your browser and subsequently stored on your hard drive. Cookies contain a unique identifier so that we can recognize your return to our site, which may then store it on your system. Some Sealevel pages may use cookies so that we may better serve you when you return to our site. You can set your browser to notify you when you receive a cookie, giving you the chance to decide whether to accept it.

Links To Other Web Sites
Sealevel’s Web site may contain links to other Web sites. While we try to link only to sites that share our high standards and respect for privacy, we are not responsible for the content or the privacy practices employed by other Web sites. If you decide to visit any linked site, you will leave this Site and will visit the linked site at your own risk.

Shipping Information
Most orders are shipped the same day (if order placed by 2:00pm EST). Lead time on shipments can range from stock to six weeks depending on quantity. A variety of shipping methods can be requested. UPS Ground insured is the standard method of shipment while UPS 3 day, 2 day or overnight, and FedEx Economy, Standard or priority can also be specified. Saturday delivery is available by both UPS and FedEx. All shipments are FOB Liberty, SC.

100% Customer Satisfaction
If you are not completely satisfied with your products you may return them for a full refund, exchange or credit within 30 days of original purchase. Returns after 30 days will be charged a 20% restocking fee. Sealevel Systems will not accept returns under the following conditions:

1. Modified products (factory or user modified)
2. Damaged products due to use negligence, misuse, modification, accident, or disaster.
3. Large volume or custom order situations. Sealevel Systems assumes that you have evaluated the products for suitability.

Any and all products returned to Sealevel Systems for any reason must be accompanied by a Return Material Authorization (RMA) Number. To obtain this number please call (864) 843-4343 and request an RMA number. You may be advised to speak to a technician to verify that an RMA is required. Please have the following information on hand when requesting your RMA number:

1. Part number of the product
2. Reason for the return
3. Name and phone number of the person requesting the RMA

Download a map with driving directions to Sealevel in PDF format. Includes information on local hotels.

Sealevel Ethernet serial servers are designed to mimic the behavior of native PC serial ports. Legacy software can communicate with the Ethernet serial server’s virtual COM port as though it was connected to a native COM port.

The Digital I/O Handbook
A Practical Guide to Industrial Input & Output Applications

Read Featured Chapters, free online.

Digital I/O Explained
Renowned technical author Jon Titus and the President and CEO of Sealevel Systems, Tom O'Hanlan, clearly explain real-world digital input/output implementation from both a hardware and software perspective. Whether you are a practicing engineer or a student, The Digital I/O Handbook will provide helpful insight you will use again and again.

• Covers a wide range of devices including optically isolated inputs, relays, and sensors
• Shows many helpful circuit diagrams and drawings
• Includes software code examples
• Presents common problems and solutions
• Detailed glossary of common industry terms
  

"What I like most is its mix of hardware and software. Most pages have a bit of code plus a schematic. All code snippets are in C. This is a great introduction to the tough subject of tying a computer to the real world. It's the sort of quick-start of real value to people with no experience in the field." - Jack Ganssle, The Embedded Muse, January, 2005.

You can purchase the Digital I/O Handbook for $19.95 by clicking here. The Digital I/O Handbook is FREE with any qualifying Sealevel Digital I/O product purchase.

Chapter Listing
Click on a chapter title link below, to read that chapter. New chapters will be released monthly, starting with the first chapter in June, 2006.

Chapter 1 - Logic Principles

• Introduction to digital electronics
• Current Sinks and sources
• Buffers and drivers
• Latches
• Negative and positive logic
• All in the family
  

Chapter 2 - Digital Outputs

• Introduction to output ports
• Simple on/off control
• Using drivers and buffers
• Relay basics
• Relays handle more power
• Optical isolation
• Solid state relays
• Control bits and bytes with software
  

Chapter 3 - Digital Inputs

• Introduction to input ports
• Basic TTL inputs
• Circuit isolation
• Current sinks and sources
• LED considerations
• Monitor high voltages
• Sense bits with software
• Flags
• Put it all together
• A final note about I/O ports
  

Chapter 4 - Sensor Interfacing

• Example 1: Thermal switch
• Example 2: Level switch
• Example 3: Hall-effect proximity switch
• Example 4: Photoelectric sensor
• Example 5: Shaft encoder
• Example 6: Output more than 8 bits
  

Appendix

• Switch and Relay Configurations

Glossary

3rd Party Software Support

Sealevel products can be used with 3rd party software packages including Testpoint, Intellution iFix, Agilent Vee, Labview, Wonderware, Labtech, Softwire, Steeplechase and Think and Do. If you don't see your software listed below, contact us and let us know. We are constantly updating our FAQ to simplify 3rd party installations.

Click to download the free Acrobat™ Reader software required for viewing these files.

	Click the appropriate link to download the PDF Application Notes Async Serial I/O with DAQ Factory - (147k) Digital I/O with DAQ Factory - (338k)
	Click to download the DASYLab Application Notes PDF - (663k)
	ENCO Corporation develops "Digital Audio Delivery" (DAD)systems that provide complete audio broadcast automation and control for television and radio broadcasters. www.enco.com
	Foxfire specializes in Warehouse Management Software solutions and services for mid-sized warehouses that want to optimize production and processes without costly custom work. www.foxfiresoftware.com
	Click here to download the Iconics Application Notes PDF -  (72k)
	Click here to download iFIX Serial I/O Application Notes PDF - (136k)
	Click here to download the LabVIEW Serial I/O Application Notes PDF - (1.1MB)
	Omnipotence Software develops the "Event Control System" (ECS)automation software for commercial, industrial, and residentialapplications. www.omnipotencesoftware.com
	SoftPLC Corporation is a specialist in PLC controls. Whether a simplemachine controller or a sophisticated, integrated factory automationsystem is required, open architecture SoftPLC's should be able to meetyour needs. www.softplc.com
	Click here to download the TALtech Application Notes PDF -  (252k)
	Click the appropriate link to download the PDF Application Notes Async Serial I/O with TestPoint -  (1.1MB) Digital I/O with TestPoint -  (1.1MB) Sync Serial I/O with TestPoint -  (1.4MB)
	WinTECH Software develops and sells a variety of diagnostic utilitiesfor industrial automation systems, including Modbus TCP and Modbus RTUtest and simulation software for 32-bit Windows and CE operatingsystems. Serial data monitor and OPC software tools are also available. www.win-tech.com
	Click the appropriate link to download PDF Application Notes Serial I/O with InControl - (1.5MB) Serial I/O with InTouch - (928k) Digital I/O with InControl - (2.2MB) Digital I/O with InTouch - (1.7MB)

Long-Term Availability
Sealevel is committed to providing our long-term availability of all of our products. In fact we still produce a variety of boards that date back to the 1980s. We work closely with our vendors to insure component availability and in instances that a component becomes obsolete we strive to design a "form, fit, and function" replacement that works transparently to the customer.

Comprehensive Software Solutions and Support
Our full array of hardware is backed by powerful software that makes implementation easy. Each Sealevel product ships with a comprehensive software suite providing drivers, setup files, samples, and application notes. Most popular operating systems are supported including Windows 95/98/ME/NT/2000/XP, QNX, and Linux. For help installing serial products, diagnostic software is supplied such as loopback tests, bit error rate testing (BERT), and throughput monitoring. All of Sealevel’s digital I/O products are now supported through our OPC driver, making connection to a variety of third-party software packages simple.

SeaI/O Software
Windows 98/ME/NT/2000/XP and Linux Digital I/O Drivers

SeaI/O includes drivers, utilities, and programming samples for Windows 98/ME/NT/2000/XP and Linux to aid in the development of reliable applications for the Sealevel Systems family of Digital I/O adapters.

The SeaI/O Windows/Linux Drivers Disk Includes:

> SeaI/O Drivers
> Windows 98/ME/NT/2000/XP Digital I/O Drivers
> Linux Digital I/O Driver
> SeaI/O Applications
> VCCTest - Visual C++ Sample with toggle switches for relays and LEDs for inputs.
> SeaIOvb - Visual Basic Sample
> SeaIOtst - Windows Console application Sample

The SeaI/O Windows/Linux Drivers are included with each Sealevel Systems Relay/Digital I/O adapter purchased. The SeaI/O Drivers have unlimited usage rights provided a Sealevel Systems hardware product is used.

Download SeaI/O Software for Windows
Download SeaI/O Software for Linux
View Sealevel Digital I/O products.

SeaI/O - Digital I/O drivers for Windows 98/ME/NT/2000/XP

The SeaI/O Windows/Linux Drivers Disk is included with all Sealevel digital I/O and relay products

SeaI/O - Applications

VCCTest - is a 32 bit Visual C++ sample with GUI (Graphical User Interface). VCCTest provides control of individual and groups of relays via toggle switches and monitoring of inputs via LEDs. VCCTest demonstrates the use of the SeaI/O API for Visual C++ Developers.

VB Test - is a 32 bit Visual Basic sample with GUI (Graphical User Interface). VB Test allows Windows control of individual and groups of relays. It offers timed relay activation and monitoring of inputs. VB Test demonstrates the use of the SeaI/O API for Visual Basic Developers.

SeaI/O Tst

SeaI/O Tst is a 32 bit Windows console application. It allows the user to exercise the functionality of the SeaI/O driver.

Supported options include:

> Up to 32 relay walk through
> Turn on all relays
> Turn off all relays
> Read inputs
> Notify of input change


Comprehensive Software Solutions and Support
Our full array of hardware is backed by powerful software that makes implementation easy. Each Sealevel product ships with a comprehensive software suite providing drivers, setup files, samples, and application notes. Most popular operating systems are supported including Windows 95/98/ME/NT/2000/XP, QNX, and Linux. For help installing serial products, diagnostic software is supplied such as loopback tests, bit error rate testing (BERT), and throughput monitoring. All of Sealevel’s digital I/O products are now supported through our OPC driver, making connection to a variety of third-party software packages simple.

SeaMAC V4 Software
Windows Synchronous Serial Drivers


SeaMAC V4
The SeaMAC V4 driver supports numerous protocols and communication methods. Certain protocols are defined well enough to allow the driver to completely handle the protocol internally. Other protocols have so many variations that creating a general driver for all cases is not practical. Sealevel's philosophy is to provide the capability (through SeaMAC V4) for the user's application to configure the driver to allow the return of meaningful data back to the application. The application can then perform any validity/integrity checking necessary on the returned data and process it as desired.  For detailed information on protocols and clocking options supported by SeaMAC V4 please visit our Sync Support page.

Customers with unique requirements are invited to contact Sealevel Technical Support or contact a Sealevel Software Partner.

Also included with SeaMAC V4 is WinSSD, a helpful utility for implementing or troubleshooting your application.

Note: Additional synchronous protocol support for a variety of legacy operating systems is available. Please call for details if you are using a legacy OS.

Download SeaMAC V4 Software for Windows
Download SeaMAC (Z85230) for Linux
Download Route56 (Z16C32) for Linux
View Synchronous Serial I/O products.

WinSSD Applications
WinSSD Ports Utility

The WinSSD Ports utility allows the user to select the COM: port number, and set the serial device type and timeouts. Status LEDs, in the application, monitor CTS, DSR, RI, and DCD. The user can also toggle RTS and DTR on output.

WinSSD Applications
WinSSD Ports Utility: Settings

On the Port Information tab, clicking the “Settings” button brings up a page that allows the user to completely configure a synchronous serial port. It allows specifying all available parameters and optionally allows saving the settings as the default for the SeaMAC V4 driver. The user has control over electrical interface, framing method, RSET and TSET source, transmitter and receiver bitrate, oscillator frequency, CRC, preamble, clock encoding, sync character, and more.

WinSSD Applications
WinSSD Loopback Test

The WinSSD Loopback Test allows functional testing of any serial port on the system, provided a loopback plug is present. WinSSD provides a pattern test, an ASCII test, and a modem control signal test. Multiple passes can be programmed to meet the user's requirements. Loopback plug diagrams are provided to aid in building loopback plugs.

WinSSD Applications
WinSSD BERT (Bit Error Rate Test)

WinSSD BERT is a multithreaded bit error rate test application for verifying serial port performance and can be used in a loopback or point-to-point configuration. This software tracks bit errors and sync losses while displaying transmit and receive frame counts, the number of bytes verified, and driver error statistics.

WinSSD Applications
WinSSD Terminal

WinSSD Terminal allows the user to select either an ASCII display, a HEX display, or a split ASCII/HEX display for data. Displaying the data onscreen can be disabled, which improves the ability to capture to a file at high data rates. The user can search through the data in the display buffer for a string of text. In addition, the user can enter a line of data to be transmitted. This data is then sent using one I/O WriteFile command. In HDLC/SDLC mode, this can be very useful when the user requires the entire string to be sent as a single frame of data.

WinSSD Applications
WinSSD Logging Options

The logging options allow the user to change the settings for the BERT and Terminal log files. The user can enable the log file to capture transmit or receive data, data size, character mismatches, sync losses, and port error messages.

SeaCOM Software
Windows 95/98/ME/NT/2000/XP Asynchronous Serial Drivers

SeaCOM provides the tools necessary to verify the installation and operation of Sealevel Systems' asynchronous serial I/O products in Windows. The Windows Serial Utility Disk is included with each Sealevel Systems' asynchronous serial I/O adapter purchased.

Driver / Utility software on the disk includes:

SeaCOM for Windows
Windows 95/98/ME/ NT/2000/XP enhanced COM drivers provide IRQ sharing, support for advanced UARTs (16650, 16750, 16850 and 16950), 9-bit data support, and Auto RS-485 RTS enable for Windows RS-485 cards without Sealevel's ULTRA hardware circuit. Advanced control panels and property pages allow specialized configuration options, further adding to the versatility of Sealevel products.

WinSSD Serial Diagnostics
WinSSD is a full featured asynchronous diagnostic utility for Windows. WinSSD allows the user modify the default UART parameters, perform external loopback tests, toggle modem control signals and transmit test pattern messages. Included applications allow terminal mode operations, bit error rate testing, and throughput monitoring.

Port Manager Utility
Port Manager is a utility included with SeaCOM that allows the user to change the Windows COM number, assign COM drivers to a specific port, and select custom data rates for Sealevel USB serial products. Port Manager is installed with each SeaCOM installation.

Download SeaCOM Drivers for Windows
Download SeaCOM Drivers for Linux
Click to view Asynchronous Serial products.

WinSSD Applications
WinSSD Ports Utility

The WinSSD Ports utility allows the user to select the COM: port number, set data rate, data bits, parity, stop bits and flow control.

WinSSD Applications
WinSSD Loopback Test

WinSSD's Loopback Test allows functional testing of any serial port on the system, provided a loopback plug is present. WinSSD provides a pattern test, an ASCII test, and a modem control signal test. Multiple passes can be programmed to meet the user's requirements. Loopback plug diagrams are provided to aid in building loopback plugs.

WinSSD Applications
WinSSD BERT (Bit Error Rate Test)

Multithreaded bit error rate test application for verifying serial port performance. WinSSD's BERT test can be used in loopback or point-to-point test configuration. This software tracks bit errors and sync losses while displaying transmit and receive frame counts, the number of bytes verified, and driver error statistics.

WinSSD Applications
WinSSD Terminal

Terminal program provided as a sample application that allows characters to be echoed back to the screen. A Hex check box is provided to allow typed characters to be echoed along with their Hex equivalents.

DOS - Serial Utility Disk
The Sealevel Serial Utility Disk provides the tools necessary to verify the installation and operation of Sealevel asynchronous serial I/O products in DOS and other non-Windows Operating Systems. The Serial Utility Disk is included with each Sealevel asynchronous serial I/O adapter purchased.

Driver / Utility software on the disk includes:

> SeaCOM for DOS - Interrupt driven DOS serial port driver
> SSD - General asynchronous diagnostic utility for DOS
> SLT - Serial loopback test program
> PCSSD - PC Card (PCMCIA) Diagnostic Menu Driven Program
> SEAPC - PC Card (PCMCIA) Client Enabler
> SSEnable - PC Card (PCMCIA) Stand Alone Card Enable Program

Supported Clocking Options and Protocols
The SeaMAC V4 driver supports numerous protocols and communication methods. The definition of some protocols is sufficient to allow the driver to completely handle the protocol internally. Others have so many variations that creating a general driver for all cases is impractical. Therefore, Sealevel’s philosophy is to provide the capability for the application to configure the driver such that the driver can return meaningful data back to an application which will then allow the application to perform any validity checking necessary on the returned data and process it as desired. Since these capabilities vary from protocol to protocol, each will be described below. In addition, a code snippet is provided for the more common variations of each protocol.

Please review the information included below carefully to determine if SeaMAC V4 will work properly for your application. If the mode of operation you require is not supported by SeaMAC V4, please contact Sealevel Technical Support for options.


General Clocking Options
One important feature of synchronous (and isochronous) communication is that a clock must exist to allow the synchronization of the data. There can be two sources of this clock. It can come from the outside world and be connected to the card’s DB25 connector, or it can be generated from the internal oscillator on the card. If it is generated internally, it must be provided to the outside world to allow other devices to know when to clock in each bit of data. This clock can either be a physically distinct signal (in addition to the data) or it can be encoded onto the data using one of many different methods. For the driver to either transmit or receive data, it needs to know which clocking method is being used. SeaMAC V4 provides for the above combinations using a few dedicated fields of the SSI_COMM_CONFIG structure.


Encoded Clock
If the clock is encoded onto the data stream, then the clock must be extracted from the stream and then used to decode the data. The device used to do this is a Digital Phase Lock Loop (DPLL). If this method is used, then the method used to encode the clock must be specified. Since a DPLL circuit must know roughly the frequency of the signal to be decoded, this information is provided in the BitRate specification. It must also know the encoding method used. This example assumes Bi-phase Space (FM0). The other options are defined in the SSI_COMM_CONFIG section of this document. This would be done by the following four statements:

CommCfg.RsetSource = ssiTimingDpll ;    // receive timing DPLL
CommCfg.TsetSource = ssiTimingDpll ;    // transmit timing DPLL
CommCfg.BitRate = 19200 ;     // transmit / receive data rate
CommCfg.ClockEncoding = ssiClockEncodingFm0 ; // Clock encoded using FM0 (Bi-phase space)

The above code assumes the transmitter would also be synchronized to the incoming receive signal. The other alternative would be to have the transmitter set to generate its own and encode its transmission based on internal clock. In this case the transmitter would be driven by the onboard oscillator (Baud Rate Generator – BRG) and the above line would be changed to read:

CommCfg.TsetSource = ssiTimingBrg ;    // transmit timing


External Clock
If the clock is not encoded onto the data stream, then it must be provided. For the receiver, the following line of code would select the mode where the clock is provided on the RXC pin(s) of the DB25 connector.

CommCfg.RsetSource = ssiTimingRxc ;    // receive timing from the DB connector on the card

For the transmitter, it is a little more complicated. The transmitter can either be clocked from an external source in which case the following lines would be used:

CommCfg.TsetSource = ssiTimingTxc ;     // transmit timing from the DB connector on the card
CommCfg.TsetFromHere = FALSE ;     // we are not providing an output clock

or the transmitter data rate can be clocked from the internal BRG in which case the lines would read:

CommCfg.TsetSource = ssiTimingBrg ;     // transmit timing from internal baud rate generator (BRG)
CommCfg.BitRate = 19200 ;     // transmit rate
CommCfg.TsetFromHere = TRUE ;     // we are providing an output clock on the TSET pins


HDLC/SDLC
This is a widely used and well-defined protocol that is almost entirely handled by the driver. Data is divided into frames consisting of a special character (called a flag), data, and another flag. The standards define that the first byte of the data portion of the frame will be an address byte, the second byte will be a control byte, and the last two bytes will optionally be a CRC. When transmitting a frame, the SeaMAC V4 driver will automatically send an opening flag, the data provided by the application, optionally calculate a CRC and send it, and then send the closing flag. It should be noted that on transmission, the address and control fields are completely ignored by the driver and just transmitted as data. The application should format the data buffer exactly as required (with the exception of the flags and CRC – note: the CRC is optional). When receiving data, it is possible for the application to specify that it wants the driver / hardware to only respond to a selected address. The driver allows the application to specify if this feature should be enabled the specification of the desired address. Note: If this feature is enabled, then all messages not containing the specified address in the first byte of the data portion of the message will be ignored.

The following is a sample of code that can be used to configure the driver for HDLC operation (It should be noted that the clocking options defined above must also have been specified):

CommCfg.Electrical = ssiElectricalRS232 ;    // Set terminated RS-232
CommCfg.Framing = ssiFramingSdlc ;     // Make sure we're using SDLC
CommCfg.CharacterSize = 8 ;     // regular 8-bit characters
CommCfg.PreTxDelayTime = 0 ;     // Transmit immediately
CommCfg.PostTxDelayTime = 0 ;     // Drop RTS immediately after closing flag
CommCfg.Loopback = FALSE ;     // no loopback
CommCfg.Echo = FALSE ;     // no echo
CommCfg.BrgSourceFromRset = FALSE ;     // bit rate from internal BRG
CommCfg.CrcPolynomial = ssiCrcCcitt ;    // normal SDLC polynomial
CommCfg.CrcPresetOnes = TRUE ;     // normal SDLC preset
CommCfg.IdleMode = ssiIdleSync ;     // idle flags between messages
CommCfg.SdlcAddressMode = ssiAddressModeFromAny ; // receive from any address
CommCfg.PreambleLength = 0 ; // no special preamble


Bisync (Binary Synchronous)
While bisync has been around for many years, many people mistakenly assume that there is a standard structure and way of automatically handling it. Unfortunately, the only thing that is absolutely defined is that a valid message will start with two sync characters (hence the name bisync).

Transmitting is more straightforward than receiving. The SeaMAC V4 driver will allow you to format a message and send it. The hardware will automatically insert the sync characters before the beginning of the message and send the data. The driver does not check for any special control characters and therefore the application can create any desired message format.

The receive side is much more complex. The first problem is synchronization. The hardware has the capability of going into “Hunt” mode. In this mode, the hardware will actually examine every bit of incoming data until if finds a 16 bit match with the specified sync characters. Because this sync pattern can exist in either a random data stream or within a valid message, it is possible for the hardware to sync at the wrong place within a data stream. SeaMAC V4 allows an application to re-enter the hunt mode at any point (see the Reference/Functions/DeviceIoControl under Contents in the help file). Once proper synchronization has been established, the question then becomes how much data to read. A normal read specifies how much data should be read and the CommTimeouts allows a timeout to occur if the requested amount of data has not arrived within a specified time period. The problem is that there is no universally accepted method of knowing when the message has ended. At the end of the message, the card goes into an idle condition. It can be either a constant stream of ones, zeros, alternating ones and zeros, sync character(s), etc. Therefore, if you do a 200 character read, and the incoming message is 6 bytes long, the read will not complete until 200 characters have come in. In this case, the data passed to the application will be 6 bytes of good data followed by 194 bytes of something else. This can be a significant problem if the receiver must either expect a long message or a short control message. If the device on the other end of the link is expecting a timely response to a control message and a large read was posted, then the other device may time out before the application receives the control message and trailing extraneous data. SeaMAC V4 attempts to address this by providing two generalized methods of handling this situation. If the framing was specified as

CommCfg.Framing = ssiFramingCharacterSync ;     // Make sure we're using unformatted bisync

this will allow the application to have full control of message processing. In situations where this poses a problem, SeaMAC V4 provides another option for detecting the end of a message and returning the data immediately to the application. To use this method, specify

CommCfg.Framing = ssiFramingCharacterSyncISO1745 ;    // Terminate on control characters

The above will notify the driver that received messages have a defined ending character. The ISO 1745 standard is a broadly used standard that uses commonly defined control characters. While we intentionally did not fully support this standard (to do so would have precluded applications having the ability to used other standards without driver modifications), we do support their control characters as message terminators. In this mode, the driver will return to the user immediately when it determines the data stream contains one of the following characters:

Character=    decimal code
ETX= 3
EOT= 4
ENQ= 5
ACK= 6
NAK= 21
ETB= 23

When transmitting, each write will be preceded by the specified sync characters and the state of the output data line between transmissions will be determined by:

CommCfg.IdleMode = ssiIdleSync ;     // idle sync character between messages
CommCfg.SyncCharacterSize = 16 ; // specify bisync(=16) as opposed to monosync(=8)
CommCfg.SyncCharacter = 0x00001610 ; // in this case, sync is ASCII DLE SYN

The above does impose the restriction that it is impossible to “merge” two outputs together to form one bisync frame using non-overlapped I/O. It is possible to merge outputs together to form one frame if the computer is fast enough to ensure the second frame has been queued to the output queue in the driver before the previous write has completed. To do this, the device must have been opened with overlapped I/O specified and the following must be specified:

CommCfg.MergeFrames = TRUE ; // attempt to send out data “back to back”


Monosync
While monosync has been around for many years, it is not nearly as widely used as bisync. A potential problem with using monosync is that the sync pattern is only 8 bits long and the possibility of syncing at the wrong place is significant.

When transmitting, the operation is almost identical to bisync except that only one sync character is generated. SeaMAC V4 will allow you to format a message and send it. The hardware will automatically insert the sync characters before the beginning of the message and send the data. SeaMAC V4 does not check for any special control characters and therefore the application can create any desired message format.

The receive side is much more complex. As with bisync, the first problem is synchronization. The hardware has the capability of going into “Hunt” mode. In this mode, the hardware will actually examine every bit of incoming data until it finds an 8-bit match with the specified sync character. Because this sync pattern can exist in either a random data stream or within a valid message, it is possible for the hardware to sync at the wrong place within a data stream. SeaMAC V4 allows an application to re-enter the hunt mode at any point (see the Reference/Functions/DeviceIoControl under Contents in the help file). Once proper synchronization has been established, the question then becomes how much data to read. A normal read specifies how much data should be read and the CommTimeouts allows a timeout to occur if the requested amount of data has not arrived within a specified time period). The problem is that there is no universally accepted method of knowing when the message has ended. At the end of the message, the card goes into an idle condition. It can be either a constant stream of ones, zeros, alternating ones and zeros, sync character(s), etc. Therefore, if you do a 200 character read, and the incoming message is 6 bytes long, the read will not complete until 200 characters have been received. In this case, the data passed to the application will be 6 bytes of valid data followed by 194 bytes of something else. This can be a significant problem if the receiver must understand various message sizes. If the device on the other end of the link is expecting a timely response to a control message and a large read was posted, then the other device may time out before the application receives the control message and trailing extraneous data. Unlike bisync mode, the driver does not support control characters to terminate the message before the character count or timeout is reached.


Raw Mode
Raw mode is a completely unformatted mode of operation used primarily for receiving although transmission is possible. In this mode, the incoming data is simply grouped into 8 bit bytes and passed to the application. There is no way to ensure any byte alignment of the incoming data. All byte alignment, sync character detection, etc. must be done entirely by the application. Since there is no way for the driver to determine when to stop, it will continue to read until the requested number of bytes have been read or a timeout period expires.

CommCfg.Framing = ssiFramingRaw ;     // Make sure we're using raw mode
CommCfg.MergeFrames = TRUE ;     // merge frames for output

Transmission is possible but has the same limitation on continuous transmission as bisync.


External Sync
External sync mode is exactly like raw mode with one exception. A sync signal must be fed into the specified pin(s) on the DB25 connector. This input signal will specify when the first bit of the first byte of the frame begins. This signal must be maintained until the last character is being received. The exact timing of this signal is defined in the Zilog Z16C32, Z85230, or Z85233 manuals. On cards based on the Zilog Z16C32, the signal should be fed into the DSR pin(s). On cards based on the Z85230/Z85233, it should be fed into the CTS pin(s). Since there is no way for the driver to determine when to stop, it will continue to read until the requested number of bytes has been read or a timeout period expires. Simply dropping the DSR signal will not terminate the read although it will stop the receiver from assembling characters.

CommCfg.Framing = ssiFramingExternalSync ;// Make sure we're using external sync mode
CommCfg.MergeFrames = TRUE ;     // merge frames for output

Transmission is possible but has the same limitation on continuous transmission as bisync.

Teligy specializes in custom device driver development and system level programming for communications and I/O hardware. Our team of development experts has years of direct experience developing custom software for Sealevel Systems' innovative I/O products. Teligy's expertise includes software development for synchronous and asynchronous communications as well as embedded systems programming on a variety of platforms.

Teligy's developers can help you customize Sealevel Systems' SeaCOM, SeaMAC, or SeaI/O drivers, port drivers to new operating systems, or create custom drivers for your project.
 
For more information or a project quote, please contact Teligy at 864.286.3856 or online at www.teligy.com

Comprehensive Software Solutions and Support
Our full array of hardware is backed by powerful software that makes implementation easy. Each Sealevel product ships with a comprehensive software suite providing drivers, setup files, samples, and application notes. Most popular operating systems are supported including Windows 95/98/ME/NT/2000/XP/Vista/7 and Linux. For help installing serial products, diagnostic software is supplied such as loopback tests, bit error rate testing (BERT), and throughput monitoring.

New! Visit our new software support sections:
Sealevel Software Partners
Sync Support - Supported Clocking Options and Protocols

Click the appropriate link below to view pages with current Drivers available for download.

SeaCOM
Windows 95/98/ME/NT/2000/XP/Vista/7 and Linux Asynchronous Serial Drivers

Our enhanced serial drivers make using our asynchronous serial products easy. In addition to Windows drivers and utilities, our SeaCOM software contains utilities, application notes, and technical details.

SeaMAC V4
Windows 2000/XP/Vista/7 and Linux Synchronous Serial Drivers

SeaMAC V4 provides a powerful WIN32 interface (CreateFile, ReadFile, WriteFile, etc) for Sealevel synchronous serial products. SeaMAC V4 supports many popular protocols including HDLC/SDLC and various bisync, monosync, and raw  (bit-shifter) modes.

SeaI/O
Windows 98/ME/NT/2000/XP and Linux Digital I/O Drivers

The SeaI/O software package is a Windows/Linux Developer's Toolkit for Sealevel Systems Relay and Digital I/O products. SeaI/O currently includes drivers for Windows 98/ME/NT/2000/XP and Linux.

Lifetime Warranty
Sealevel's commitment to providing the best I/O solutions is reflected in the Lifetime Warranty that is standard on all Sealevel manufactured I/O products. Relio™ industrial computers are warranted for a period of two years from date of purchase. We are able to offer this warranty due to our control of manufacturing quality and the historically high reliability of our products in the field. Sealevel products are designed and manufactured at its Liberty, South Carolina facility, allowing direct control over product development, production, burn-in and testing.Sealevel achieved ISO-9001:2000 certification in 2002.

Warranty Policy
Sealevel Systems, Inc. (hereafter "Sealevel") warrants that the Product shall conform to and perform in accordance with published technical specifications and shall be free of defects in materials and workmanship for the warranty period. In the event of failure, Sealevel will repair or replace the product at Sealevel's sole discretion. Failures resulting from misapplication or misuse of the Product, failure to adhere to any specifications or instructions, or failure resulting from neglect, abuse, accidents, or acts of nature are not covered under this warranty.

Warranty service may be obtained by delivering the Product to Sealevel and providing proof of purchase. Customer agrees to insure the Product or assume the risk of loss or damage in transit, to prepay shipping charges to Sealevel, and to use the original shipping container or equivalent. Warranty is valid only for original purchaser and is not transferable.

This warranty applies to Sealevel manufactured Product. Product purchased through Sealevel but manufactured by a third party will retain the original manufacturer's warranty.

Non-Warranty Repair/Retest
Products returned due to damage or misuse and Products retested with no problem found are subject to repair/retest charges. A purchase order or credit card number and authorization must be provided in order to obtain an RMA (Return Merchandise Authorization) number prior to returning Product.

SeaMAC V4 automatically installs application samples with source code in the 'Samples' subdirectory.

In Windows 2000, XP, and Vista, samples are located on your hard drive under C:\Program Files\SeaMAC V4\Samples\.

Sealevel provides WinSSD, a helpful software utility that allows easy verification your synchronous card is working properly. After you install the SeaMAC V4 synchronous software driver onto your system, WinSSD will be located in the SeaMAC folder in the Start menu.

To verify operation of your card, launch WinSSD, open the port and then select RS-232 as your electrical interface. Configure RSET source and TSET source for "SSI Timing BRG" and attach a Sealevel loopback or jumper wire between Tx and Rx (pins 2 & 3). Use the BERT test (Bit Error Rate Test) in the WinSSD application, which will transmit and receive data to confirm that the synchronous serial card is working correctly.

Sealevel synchronous serial products fall into three categories: ZiLOG Z16C32 based devices, ZiLOG Z85230 based devices and older ISA DMA channel cards.

The fastest family of Sealevel synchronous serial products is built around the ZiLOG Z16C32 IUSC which has an onboard DMA controller. All Sealevel Z16C32 based products have 256K of onboard RAM that is mapped to the PC's internal memory. Using the SeaMAC V4 driver, the onboard DMA controller allows these products to achieve burst rates of 10 Mbps and sustained data rates of up to 6 Mbps.

The Sealevel synchronous serial products built around the ZiLOG Z85230 ESCC are supported by the SeaMAC V4 driver in interrupt mode. These products make use of the small onboard FIFO (8 byte receive, 4 byte transmit) in the ZiLOG Z85230 to achieve a maximum burst data rate of 128 Kbps with a sustained data rate of up to 56 Kbps.

The older ISA DMA channel synchronous serial cards are built around the ZiLOG Z85230 ESCC. Using the SeaMAC V4 driver, these cards operate in interrupt mode and are limited to a maximum burst data rate of 128 Kbps with a sustained data rate of up to 56 Kbps.

Sealevel provides a synchronous serial driver, SeaMAC V4, to interface our synchronous serial adapters to your computer. To access the cards from your application program, you will use the SeaMAC API (Application Programmer Interface).

To locate the configuration settings for the SeaMAC API in Windows 2000, XP or Vista, start by installing the SeaMAC V4 driver. Click Start > All Programs > SeaMAC V4 > and launch 'SeaMAC V4 Help'. When the help window opens, expand 'Reference' and then expand 'Structures'. Review the DCB and COMMTIMEOUTS and SSI_COMM_CONFIG sections. Both explain the various configuration parameters for the SeaMAC device.

For Sealevel synchronous serial products, after connecting the Transmit (TX) and Receive (RX) pins, you will need to connect the Clock Output pin (TSET) to the Clock Input pin (RXC). In most cases, the Clock Output pin (TSET) should be used as the board's output clock. Transmit Clock (TXC) is an input and should not be used.

The Z85230 PDF user manual and the Z16C32 PDF user manual are both available on the ZiLOG web site and are used on a variety of Sealevel synchronous serial products.

The SeaIO software package automatically installs several application samples with source code in the Samples subdirectory.

To access to the samples, navigate to: [main drive]:\Program Files\SeaIO\Samples. For a listing and description of the samples, refer to the help file located at: Start > All Programs > SeaIO.

This is located in the help file when SeaIO software is installed. From the Start menu, locate the SeaIO folder and choose SeaIO Help. In the contents you will find a section titled Programmers Interface. This will explain the Usage and API references that fully document the SeaI/O API, including samples and descriptions of all calls.

Sealevel Digital I/O products with reed relays are not designed to switch inductive loads such as the coil on another relay. If you need to switch an inductive load, Sealevel recommends using a Digital I/O product with Form C relays instead. You should remember to place a diode parallel to the coil to suppress the inductive kickback voltage. Failing to install a diode will shorten the life of the relay contacts.

Yes. Supporting documentation is located in the help file when SeaIO software is installed. From the Start menu, locate the SeaIO folder and choose SeaIO Help. In the contents you will find a section titled "Active X Controls" that explains the Properties, Methods and Events for Active X I/O control.

Sealevel offers Digital I/O TTL products that interface to industry standard relay racks and solid state relay modules that are designed to sense and switch AC voltages. Relay racks with solid state relay modules are also ideal for switching other relays and inductive loads.

Overview

A world leading developer and manufacturer of critical two-way radio communications systems used by public safety and government organizations such as police and fire departments needed an ultra-reliable industrial computer to monitor remote site operations. Sealevel designed a custom Relio system to monitor all critical sitefunctions and trigger alarms before communication can be jeopardized. Reliability is paramount since the systems may be deployed in remote locations such as mountaintops, deserts, and swamps where a service call would be time-consuming and extremely expensive.

See how Sealevel engineers were able to incorporate 120 optically isolated inputs, 96 digital outputs, 40 12-bit A/D channels, and serial, USB, and Ethernet functionality into a custom solid-state, industrial computing solution. All of this I/O and standard PC interfaces fits in a fanless 1U rackmount chassis. Download the rest of the "Customer Spotlight - Relio™ Emergency Communications" article (520kb printer-friendly PDF), below. Sealevel also offers a variety of standard Industrial Computing solutions.

Overview

A leading radio broadcasting company required a reliable, small, cost-effective solution for monitoring and control at radio transmitter sites. In addition to the dense I/O requirements, the customer requested that the design allow for easy upgrade or replacement of the single board computer. Sealevel designed a custom Relio system providing a variety of serial, analog, and digital I/O that can be queried or send alerts via the internet or a standard telephone connection. The system supports Windows XP or Linux and the design includes 64 optically isolated inputs, 64 digital outputs, 24 14-bit analog inputs, voice modem with DTMF, serial, USB, and Ethernet functionality in a 1U rackmount enclosure.

Download the rest of the "Customer Spotlight – Relio™ Radio Transmission Supervisory System" article (865kb printer-friendly PDF), below the image, for complete details on how Sealevel engineers solved the challenges presented by this application. Sealevel also offers a variety of standard Industrial Computing solutions.

Overview

A leading manufacturer of semiconductor fabrication equipment needed to communicate with a large number of serial devices from an industrial computer running their process control software. They preferred using the system’s USB port, but required isolation to protect the computer from potentially harmful voltage spikes. Sealevel leveraged our expertise in USB and serial connectivity to design a custom isolated USB to 16 port serial solution.

See how Sealevel engineers designed a 16 port RS-232 serial device, with an isolated USB connection to the host, and delivered working prototypes in only six weeks. That short timeframe includes designing a new rugged, metal, 1U rackmount enclosure. Download the rest of the "Customer Spotlight - Isolated USB to 16 Serial Ports" article (881kb printer-friendly PDF), below the image. Sealevel also offers a variety of standard USB to Serial products.

Overview

The first Relio system was designed as a remote data acquisition component of an OEM Enterprise Management System. Vital systems and infrastructures require constant monitoring and vigilant management to stay online and available. The Relio automatically collects and sends data from critical infrastructure devices such as UPS, generator, and power distribution units and communicates that data, as well as status and alarms, back to the centrally located enterprise server that analyzes the information. The Relio can operate independently and generate alarms even if the connection to the central server is unavailable, increasing the overall availability of the management system.

See how Sealevel engineers met the design challenge by offering flexible PC/104 I/O expansion in a solid-state 2U industrial computing solution. Download the rest of the "Customer Spotlight - Relio™ Facility Management" article (1.3mb printer-friendly PDF), below the image. Sealevel also offers a variety of standard Industrial Computing solutions.

Overview

A manufacturer of security systems for public facilities required a 2U rackmount computer with a large amount of I/O to interface a variety of motors and sensors. The new system based on the Relio platform replaces a PLC and several discrete I/O modules. The design results in more flexible programming capabilities and lower cost while maintaining the reliability that is crucial to the system.

See how Sealevel engineers incorporated 32 optically isolated inputs, 32 relay outputs, A/D, D/A, and fieldbus functionality into a custom 1U industrial computing chassis. Download the rest of the "Customer Spotlight - Relio™ Public Security Systems" article (1.2mb printer-friendly PDF), below the image. Sealevel also offers a variety of standard Industrial Computing solutions.

Overview

A nationwide provider of healthcare equipment used in hospitals needed a serial I/O intensive computing solution for the redesign of a critical care monitoring system. In their application, a monitoring device provides patient information via RS-485 that must be received and archived by a central server. To avoid the cost of a computer in each room, the system must interface up to 16 patient rooms, timestamp the data, and then upload the information to the server. The system, running Windows CE, incorporates 16  two-wire RS-485 ports with RJ45 connectors. To power peripheral devices, 24V power is passed through pin 5 of each RJ45 port. The design also includes 10/100BaseT Ethernet, analog video, an externally accessible CompactFlash socket, and other standard PC functionality in a 1U rackmount chassis.

Download the rest of the "Customer Spotlight – Relio™ Patient Monitoring System" article (651kb printer-friendly PDF), below the image, for complete details on how Sealevel engineers overcame mechanical and software design challenges with this important system. Sealevel also offers a variety of standard Industrial Computing solutions.

Overview

A customer designing a new hazardous area computer system required all external connections to the host to be isolated in order to meet certification requirements. The single board computer used in the system provided the USB, RS-232, and RS-422 functionality needed by the customer, but these ports were not isolated. In a very short time frame, Sealevel designed a custom board that isolated these signals and routed them to the connectors mounted in the system enclosure via ribbon cables.

See how Sealevel engineers successfully tackled the tough challenge of designing a board small enough to fit into the space available in the customer's enclosure, yet still provide electrical isolation for three signal interfaces: USB, RS-232, and RS-422. Download the rest of the "Customer Spotlight - Custom Serial Isolation Board" article (722kb printer-friendly PDF), below the image. Sealevel also offers a variety of standard USB to Serial products.

Overview

A leading military contractor performing diagnostic testing and calibration functions on aircraft wanted to reduce the number of physical connections required for their test computer. The contractor was using a combination of Ethernet, serial and digital I/O interfaces between their test computer and aircraft transport rack (ATR). The contractor wanted to limit the costs associated with a custom design by leveraging as much off-the-shelf material and products as possible. The interface solution needed to mount in an existing 19" rack using the 2U (3.5") space available and have as few connections to the test computer as possible.

Sealevel customized a solution that reduced the connections to the test computer to one USB cable and one Ethernet cable. A standard 2U Relio industrial computer chassis houses off-the-shelf SeaI/O data acquisition modules and a common industrial Ethernet switch. The interface to the ATR is via a military-style 128-pin connector.

Download the rest of the "Custom Solutions - Aircraft Test Interface" article (1.4mb printer-friendly PDF), below the image.

Our core expertise with serial and digital I/O gives us an unmatched advantage to tackle difficult challenges and provide innovative solutions. In this example, we delivered a custom solution with off-the-shelf products that included our popular SeaI/O data acquisition modules. Call us to discuss how we can build a "custom" off-the-shelf solution for you.

Overview

A leading supplier of emergency notification system used by private and governmental entities, nuclear plants, and chemical stockpile (CSEPP) sites around the country contracted Sealevel to design a custom Relio to power their newest product introduction. Upon occurrence of an event, the system can notify appropriate agencies via telephone and also perform a variety of other actions including activating warning sirens, opening, closing, locking, and unlocking doors, controlling traffic signals, and turning on or off HVAC systems.

See how Sealevel engineers incorporated DTMF and other event monitoring capabilities into a custom solid-state, 1U industrial computing chassis. Download the rest of the "Customer Spotlight - Relio™ Emergency Alert & Notification" article (529kb printer-friendly PDF), below the image. Sealevel also offers a variety of standard Industrial Computing solutions.

RoHS/WEEE Compliance & Green Initiatives

• RoHS/WEEE Compliance
• Steps To Achieving RoHS Compliance
• All RoHS Compliant Products Are Not Created Equal
• RoHS Compliance Identification
• Industry's First RoHS-Compliant Low Profile PCI RS-232/422/485/530 Board
• Industry's First RoHS-Compliant Low Profile PCI Digital I/O Board
• Popular PCI RS-232/422/485 Board Achieves RoHS Compliance
• WEEE Compliance Identification
• Article Reprints
• Glossary
  

RoHS/WEEE Compliance
Sealevel Systems is committed to providing our customers with high quality products that meet the RoHS (2002/95/EC), WEEE (2002/96/EC), and other green initiatives being adopted by the global community. The RoHS directive restricts the use of lead and certain other hazardous materials in electronic products marketed to the European Union. Sealevel is designing all new products for RoHS compatibility as well as modifying legacy products and manufacturing processes for RoHS compliance. We will continue to offer both RoHS compliant and non-compliant products to meet global and domestic customer demand.

Steps To Achieving RoHS Compliance
In order to comply with the RoHS directive, Sealevel engineers had to reconsider every step of the manufacturing process including:

• Eliminating banned substances
• Selecting PC board laminate materials lead-free solders
• Confirming compliant components availability and cost
• Awareness of higher manufacturing temperatures
• Choosing metal and plastic enclosure materials
• Specifying paint, silkscreen, and powder-coating materials
• Establishing benchmarks for Tg, CTE, and Td
• Identifying and stocking compliant and noncompliant products
• Considering long-term reliability of products
  

All RoHS Compliant Products Are Not Created Equal
To comply with the RoHS directive, Sealevel had to change the soldering processes used in manufacturing. Lead-free solders, called SAC alloys, must be used and they have a significantly higher melting point than lead alloy solders. PC boards are made using a laminate material consisting of a resin or epoxy reinforced by glass fibers. The higher manufacturing temperatures change the integrity of traditional laminate materials causing them to expand and/or delaminate. While most laminate materials were already RoHS compliant, commonly used board materials can’t withstand the higher manufacturing temperatures required by using lead-free solder. Other manufacturers have neglected this fact and continue to use traditional PC board laminate materials. Sealevel tested several laminate materials and developed prototype boards that were subjected to numerous thermal cycles over the course of several weeks, from temperatures as low as –40°C to as high as +100°C. Sealevel selected a laminate material that could handle the higher manufacturing temperatures and still be cost effective for our customers. Although extreme, these tests confirm the exceptional reliability of the products for which Sealevel is known.

RoHS Compliance Identification
Electronic products sold into the European Union must be free of six hazardous substances by July 1, 2006, as stated in Directive 2002/95/EC. RoHS compliance comes at a premium and because many customers still demand non-compliant products, Sealevel devised a unique and ingenious identification method. All new Sealevel circuit boards will have two gold-plated, etched-copper pads marked "RoHS" and "non-RoHS" in the silkscreen. The absence of these pads denotes a non-compliant product. During separate manufacturing processes, compliant boards will have a solder mark on the "RoHS" pad, while non-compliant boards will have a solder mark on the "non-RoHS" pad. Thus, the boards are clearly marked and can be visually identified.

Since compliant and noncompliant products share a common design, Sealevel chose to continue with the familiar 4-digit part numbering scheme for non-compliant products. RoHS compliant parts will append "-RoHS" to the end of the part number. Only after Sealevel could finally guarantee the reliability did we announce new industry-first RoHS compliant products.

Industry’s First RoHS-Compliant Low Profile PCI RS-232/422/485/530 Board
On 11/18/2005, Sealevel Systems, Inc. announced the first RoHS-compliant multi-interface PCI serial I/O card, the 7106-RoHS. The board offers a selectable RS-232, RS-422, RS-485, or RS-530 interface and is MD1 low profile and universal bus compatible (3.3V or 5V). The 7106-RoHS was the first in a series of forthcoming RoHS-compliant serial product introductions.

Industry’s First RoHS-Compliant Low Profile PCI Digital I/O Board
On 12/9/2005, Sealevel Systems, Inc. announced the first RoHS-compliant low profile PCI digital I/O adapter, the 8018-RoHS. The board offers easy connection to industry-standard solid-state relay racks for monitoring and control of AC and DC signals. Designed for compatibility with legacy and new computer systems, the board is MD1 low profile and universal bus compatible (3.3V or 5V). The 8018-RoHS was the first in a series of forthcoming RoHS-compliant digital I/O product introductions.

Popular PCI RS-232/422/485 Board Achieves RoHS Compliance
Sealevel's popular 7201 board is now RoHS compliant with the introduction of the 7201-RoHS. The board provides two serial ports, each individually configurable for RS-232, RS-422, or RS-485. The 7201-RoHS is capable of data rates to 460.8K bps and automatically handles RS-485 transmitter enable/disable. The board utilizes 16C850 UARTs that provide 128-byte Tx/Rx FIFOs and is Universal Bus (3.3V or 5V) compatible.

WEEE Compliance Identification
Legislation enacted on August 13, 2005, requires electronic product manufacturers that ship to the European Union to provide a means for recycling materials as stated in Directive 2002/96/EC. All WEEE compliant products are denoted by a trash receptacle icon with an 'X' through it. For questions about Sealevel’s recycling policy, please send an email to sales@sealevel.com.

Article Reprints

• Lead Makes An Electronic Exit (741K PDF, download below) - Test & Measurement World, 3/2006 - Martin Rowe

Glossary

Lead – Pb
A naturally occurring metallic element, lead is commonly found in the tin/lead solder traditionally used to mount components to circuit boards. Lead was commonly used in many electronic components, but is rapidly being phased out by the global community.

Cadmium – Cd
A naturally occurring metallic element, cadmium is commonly used in Nickel-Cadmium (NiCd) batteries and certain solders. It is also used for plating contacts, pigmenting components, stabilizing PVC plastics, and as a doping material in avalanche photodiodes.

Hexavalent Chromium – CrVI or Cr6
Chromium is a naturally occurring metallic element that exists in several forms, yet only hexavalent chromium is recognized as hazardous. It is commonly used as a dye or pigment in paints, inks, and plastics. It’s also used as an anti-corrosion agent to protect metal surfaces prior to painting or powder coating.

Mercury – Hg
The only metal liquid at room temperature, mercury is an element extracted from cinnabar ore. It is found in some metal alloys, mercury switches, mercury-wetted relays, some batteries, and many other compounds. It also has many common uses outside of the electronics industry.

Polybrominated Biphenyls – PBB
Polybrominated Diphenyl Ethers – PBDE
A family of compounds sold under a variety of trade names and primarily used as a flame retardant in molded thermoplastics and PC board laminates.

Coefficient of Thermal Expansion – CTE
The measurement of how much a PC board laminate will expand in the Z-axis (thickness) when exposed to the high manufacturing temperatures required using RoHS compliant materials. The danger is that as the laminate increases, the barrels (interconnects between PC board layers) can crack, causing an open or even worse, an intermittent open. Many other manufacturers are focusing only on Tg, but CTE and Td are equally important metrics. Expressed in parts-per-million per degree Celsius (ppm/°C), the CTE should be as low as possible. The maximum CTE allowed by Sealevel for laminate materials is 65ppm/°C, although 45ppm/°C has been achieved.

Laminate Materials
Most commercially available PC boards are made using a laminate material that consists of fiberglass reinforced resin or epoxy. Modern PC boards contain multiple layers of laminate material enclosing internal traces (also called circuits) as well as those visible on both external surfaces. Due to the higher heat requirements of manufacturing using lead-free solder, the interconnects (called vias) between the different layers are prone to cracking. The cracks can cause intermittent failures that are hard to diagnose. This is what makes the Tg, CTE, and Td metrics so important when considering new laminate materials.

Lead-Free Solder
Referred to as a SAC alloy by its composition of Tin (Sn), Silver (Ag), and Copper (Cu), Sealevel has adopted SAC305 as the solder used in our manufacturing process. This SAC alloy was selected by NEMI (National Electronics Manufacturing Initiative) and is recognized as the alloy of choice by the IPC (Association Connecting Electronics Industries). SAC305 has a melting point of 217°C, as opposed to 183°C for traditional tin/lead solder. A completely new reflow process was required to use this new solder.

PC Board - PCB
Refers to a 'printed circuit board'

RoHS Directive
Click the link to read the complete RoHS 2002/95/EC Directive. This will open the complete five-page PDF (116k) document in a new browser window. You may need to disable pop-up blockers, or you can right-click and save the file to your hard drive.

Thermal Decomposition Temperature – Td
A measurement of the physical degradation of a laminate material calculated based on the temperature at which the sample of laminate material loses 5% of its weight. Expressed in degrees Celsius (°C), the Td should be significantly higher than the maximum exposure temperature of the laminate material during the manufacturing process. The minimum Td allowed by Sealevel is 350°C. Many other manufacturers are focusing only on Tg, but Td and CTE are equally important metrics.

Glass Transition Temperature – Tg
The measurement of the temperature at which a laminate material changes from a semi-rigid state to a softened (rubbery) state. It is a given that the Tg of a laminate material will be exceeded during the manufacturing process. Sealevel had to first consider the magnitude of the difference between the exposure temperature and Tg of various laminate materials. Manufacturing processes had to be developed to minimize the time the Tg is exceeded. Expressed in degrees Celsius (°C), the minimum Tg allowed by Sealevel is 175°C, with the goal of finding laminate materials with a higher Tg at a reasonable cost. Many other manufacturers are focusing only on Tg, but Td and CTE are equally important metrics.

WEEE Directive
Click to read the complete WEEE 2002/96/EC Directive. This will open the complete fifteen-page PDF (288k) document in a new browser window. You may need to disable pop-up blockers, or you can right-click and save the file to your hard drive.

Please check out the Sealevel Green Commitment page for more information.

The Problem: The USB Interface Was Not Designed for Industrial Environments

The USB interface was originally designed to give home computer users a universal method for connecting peripherals. Over time, USB has become the most common interface and has migrated to products targeting industrial applications.However, the USB mechanical connector was designed to be quickly connected and disconnected and did not include a locking mechanism. As a result, accidental cable disconnection is the single most common point of failure with USB industrial I/O devices.

The Solution: Sealevel SeaLATCH Connectors Provide a Secure USB Connection

The thumbscrew on a SeaLATCH USB cable provides a secure metal-to-metal connection preventing accidental disconnection. Patent-pending SeaLATCH connectors are fully compatible with standard USB cables.

Sealevel incorporates SeaLATCH locking USB ports (shown below) on many Sealevel USB I/O devices.

Sealevel SeaLATCH Locking USB Cables

Item# CA332 – 72" USB cable with both SeaLATCH type A and type B USB connectors
The CA332 secures both ends of the cable to devices with SeaLATCH locking USB ports and offers complete protection against accidental cable disconnection.

Item# CA356 – 72" USB cable with SeaLATCH type B and standard type A connectors
The CA356 provides a secure connection between Sealevel products with a SeaLATCH type B USB port and legacy USB products with a standard USB type A port. This cable is included with Sealevel devices that have a SeaLATCH type B USB port.

Item# CA355 – 72" USB cable with standard type B and SeaLATCH type A connectors
The CA355 provides a secure connection between legacy USB products with a standard USB type B port and Sealevel products with a SeaLATCH USB type A port. This optional cable is ideal for use with Sealevel’s optically isolated USB hub (Item# 270U) and Relio industrial computers incorporating the SeaLATCH USB type A port.

SeaLATCH locking USB cables are fully compatible with standard USB cables. If a SeaLATCH USB cable is lost or damaged, any standard USB cable can be used in its place.

Sealevel Products with SeaLATCH Locking USB Ports

Sealevel USB products allow you to monitor and control serial and digital I/O from any USB-equipped computer. SeaLATCH locking USB ports are integrated into a number of products including an isolated USB hub (Item# 270U), the popular SeaI/O USB family of data acquisition modules, and industrial computers. Look for SeaLATCH ports on all future Sealevel USB I/O products.

• SeaI/O SeaLATCH Equipped Isolated USB Hub
Voltage spikes, power surges, and ground loops that affect traditional serial interfaces also affect USB devices. The SeaI/O-270U is an optically isolated USB hub that connects up to seven USB peripherals and protects the host computer from voltages up to 1500 VAC.

SeaI/O-270U – Optically Isolated 7-Port USB Hub

• SeaI/O SeaLATCH Equipped USB Data Acquisition Modules
Sealevel's USB SeaI/O data acquisition modules provide powerful digital, analog, and serial expansion to any computer allowing you to add the functionality required for your particular application. Multiple units can be daisy chained using convenient pass-through connectors to create a versatile distributed control and monitoring network.

SeaI/O-410U – 16 Isolated Inputs and 16 Reed Relay Outputs
SeaI/O-420U – 16 Isolated Inputs and 8 Form C Relay Outputs
SeaI/O-430U – 32 Optically Isolated Inputs
SeaI/O-440U – 32 Reed Relay Outputs
SeaI/O-450U – 16 Form C Relay Outputs
SeaI/O-462U – 96 Channel TTL Digital Interface (DB78)
SeaI/O-463U – 96 Channel TTL Digital Interface (IDC50)
SeaI/O-470U – 16 A/D, 2 D/A, 8 24V Output, 8 Isolated Inputs Multifunction Interface
SeaI/O-520U – 8 Isolated Inputs and 8 High-Current Form C Relay Outputs

• SeaI/O SeaLATCH Equipped USB Serial Expansion Modules
SeaI/O USB serial expansion modules provide an easy way to add multiple serial ports to a host via the popular SeaI/O module footprint. Serial expansion modules are offered with four or eight serial ports, and external power is fused and connected to pin 5 on each of the RJ45 connectors for conveniently powering serial peripherals. SeaI/O USB serial expansion modules are perfect for adding serial ports to a SeaI/O data acquisition "stack" or a Relio R1000 embedded solid-state industrial computer.

SeaI/O-641U – 4-Port RS-232 RJ45 Serial Interface
SeaI/O-647U – 4-Port RS-232, RS-485 RJ45 VersaCom Serial Interface
SeaI/O-681U – 8-Port RS-232 RJ45 Serial Interface
SeaI/O-687U – 8-Port RS-232, RS-485 RJ45 VersaCom Serial Interface

• SeaDAC Lite SeaLATCH Equipped USB Digital I/O Modules
SeaDAC Lite USB digital I/O modules provide a low I/O count solution in a small, rugged enclosure. Models are available with optically isolated inputs and Reed or Form C relay outputs. SeaDAC Lite modules are powered by the USB port, eliminating external power supplies.

SeaDAC Lite DIO-8 - 4 Optically Isolated Inputs / 4 Reed Relay Outputs
SeaDAC Lite PLC-8 - 4 Optically Isolated Inputs / 4 Form C Relay Outputs
SeaDAC Lite ISO-4 - 4 Optically Isolated Inputs
SeaDAC Lite REL-4 - 4 Reed Relay Outputs
SeaDAC Lite REL-4C - 4 Form C Relay Outputs

• SeaLINK SeaLATCH Equipped USB DIN Rail Serial Adapters
Offering designers the choice of one or two serial ports, SeaLINK serial devices are the perfect way to connect peripherals such as barcode scanners, serial displays, and data acquisition modules to any USB port. Each DB9M serial port is configurable for RS-232, RS-422, or RS-485 via dip switches accessible through the case, and optical isolation protects the host computer from damaging voltage surges and ground loops commonly found in industrial and OEM applications.

SeaLINK+I.DIN - Isolated 1-Port RS-232/422/485 Serial Interface Adapter
SeaLINK+2I.DIN - Isolated 2-Port RS-232/422/485 Serial Interface Adapter

(Coming Soon!) Sealevel SeaLATCH Equipped USB Products

Sealevel is developing new products with SeaLATCH locking USB ports. Look for SeaLATCH locking USB connectors on new serial adapters, digital I/O modules, industrial computers and touchscreen HMI solutions. Subscribe to our monthly newsletter and stay informed as we release new products.

Invitation to OEM Manufacturers to Adopt SeaLATCH USB Design

Sealevel invites OEM manufacturers to adopt SeaLATCH locking USB ports and cables in your hardware designs. If you’re interested in integrating SeaLATCH USB ports into your enclosure or purchasing SeaLATCH USB cables, contact Sealevel for more information. Custom length SeaLATCH locking USB cables are also available for OEM customers with low minimum order quantities, call +1 (864) 843-4343 (USA) for details.

Asynchronous Communications Overview
Asynchronous communications is the standard means of serial data communication for PC compatibles and PS/2 computers. Serial data communications implies that individual bits of a character are transmitted consecutively to a receiver that assembles the bits back into a character. Data rate, error checking, handshaking, and character framing (start and stop bits) are predefined and must correspond at both the transmitting and receiving ends. Serial asynchronous communications is typically implemented with a Recommended Standard (RS). The standard usually defines signal levels, maximum bandwidth, connector pin-out, supported handshaking signals, drive capabilities, and electrical characteristics of the serial lines. The following sections briefly describe some of the more common communication standards. Voltage levels that are stated are typical and may vary due to line characteristics. All interfaces accept a range of acceptable electrical and physical parameters and may even operate in excess to the specified standard under certain line characteristics. The full specification for each standard is available from almost any dealer of engineering documents. For a more detailed explanation of asynchronous serial communications, Sealevel technical support recommends the book Technical Aspects of Data Communications by John E. McNamara, published by Digital Press (DEC) 1982.

Synchronous Communications Overview
"Synchronous Communications is used for applications that require higher data rates and greater error checking procedures. Character synchronization and bit duration are handled differently than asynchronous communications. Bit duration in synchronous communications is not necessarily predefined at both the transmitting and receiving ends. Typically, a clock signal is provided in addition to the data signal. This clock signal will mark the beginning of a bit cell on a predefined transmission. The source of the clock is predetermined and sometimes multiple clock signals are available. For example, if two nodes want to establish synchronous communications, point A could supply a clock to point B that would define all bit boundaries that A transmitted to B. Point B could also supply a clock to point A that would correspond to the data that A received from B. This example demonstrates how communications could take place between two nodes at completely different data rates.

Character synchronization with synchronous communications is also very different from the asynchronous method of using start and stop bits to define the beginning and end of a character. When using synchronous communications, a predefined character or sequence of characters is used to let the receiving end know when to start character assembly. This predefined character is called a sync character or sync flag. Once the sync flag is received, the communications device will start character assembly. Sync characters are typically transmitted while the communications line is idle or immediately before a block of information is transmitted. To illustrate with an example, let's assume that we are communicating using eight bits per character. Point A is receiving a clock from point B and sampling the receive data pin on every upward clock transition. Once point A receives the pre-defined bit pattern (sync flag), the next eight bits are assembled into a valid character. The following eight bits are also assembled into a character. This assembly will repeat until another pre-defined sequence of bits is received (either another sync flag or a bit combination that signals the end of the text, i.e., EOT). The actual sync flag and protocol varies depending on the sync format (SDLC, BISYNC, etc.).

Serial communications, synchronous or asynchronous is typically implemented with a Recommended Standard (RS). In most cases, the standard is set by the Electronic Industries Association (EIA). The standard usually defines signal levels, maximum bandwidth, connector pin-out, supported handshaking signals, drive capabilities, and electrical characteristics of the serial lines. The following section briefly describes some of the more common communication standards. Voltage levels stated are typical and may vary due to line characteristics. All interfaces accept a range of acceptable electrical and physical parameters and may even operate in excess to the specified standard under certain line characteristics. The full specification for each standard is available from a number of engineering document dealers. For a detailed explanation of serial communications, please refer to the book Technical Aspects of Data Communications by John E. McNamara, published by Digital Press (DEC) 1982."

Electrical Interface Standards

RS-232
Probably the most widely used communication standard is RS-232. This implementation has been defined and revised several times and is often referred to as RS-232C or EIA-232. The most common implementation of RS-232 is on a standard 25 pin D sub connector, although the IBM PC computer defined the RS-232 port on a 9 pin D sub connector. Both implementations are in wide spread use. RS-232 is capable of operating at data rates up to 20 Kbps / 50 ft. The absolute maximum data rate may vary due to line conditions and cable lengths. RS-232 often operates at 38.4 Kbps over very short distances. The voltage levels defined by RS-232 range from -12 to +12 volts. RS-232 is a single ended interface, meaning that a single electrical signal is compared to a common signal (ground) to determine binary logic states. A voltage of +12 volts (usually +3 to +10 volts) represents a binary 0 and -12 volts (-3 to -10 volts) denotes a binary 1.

RS-422
The RS-422 specification defines the electrical characteristics of balanced voltage digital interface circuits. RS-422 is a differential interface that defines voltage levels and driver / receiver electrical specifications. On a differential interface, logic levels are defined by the difference in voltage between a pair of outputs or inputs. In contrast, a single ended interface, for example RS-232, defines the logic levels as the difference in voltage between a single signal and a common ground connection. Differential interfaces are typically more immune to noise or voltage spikes that may occur on the communication lines. Differential interfaces also have greater drive capabilities that allow for longer cable lengths. RS-422 is rated up to 10 Megabits per second and can have cabling 4000 feet long. RS-422 also defines driver and receiver electrical characteristics that will allow 1 driver and up to 32 receivers on the line at once. RS-422 signal levels range from 0 to +5 volts. RS-422 does not define a physical connector.

RS-423
The RS-423 specification defines the electrical characteristics of unbalanced voltage digital interface circuits. The voltage levels defined by RS-423 range from -5 to +5 volts. RS-423 is a single ended interface, meaning that a single electrical signal is compared to a common signal (ground) to determine binary logic states. A voltage of +5 volts represents a binary 0 and -5 volts denotes a binary 1. RS-423 is rated up to 100K bits per second. RS-423 defines driver and receiver electrical characteristics. RS-423 does not define a physical connector.

RS-449
RS-449 (a.k.a. EIA-449) compatibility means that RS-422 signal levels are met, and the pin-out for the DB-37 connector is specified. The EIA (Electronic Industry Association) created the RS-449 specification to detail the pin-out, and define a full set of modem control signals that can be used for regulating flow control and line status.

RS-485
RS-485 is backwardly compatible with RS-422; however, it is optimized for partyline or multi-drop applications. The output of the RS-422/485 driver is capable of being Active (enabled) or Tri-State (disabled). This capability allows multiple ports to be connected in a multi-drop bus and selectively polled. RS-485 allows cable lengths up to 4000 feet and data rates up to 10 Megabits per second. The signal levels for RS-485 are the same as those defined by RS-422. RS-485 has electrical characteristics that allow for 32 drivers and 32 receivers to be connected to one line. This interface is ideal for multi-drop or network environments. RS-485 tri-state driver (not dual-state) will allow the electrical presence of the driver to be removed from the line. The driver is in a tri-state or high impedance condition when this occurs. Only one driver may be active at a time and the other driver(s) must be tri-stated. The output modem control signal Request to Send (RTS) controls the state of the driver. Some communication software packages refer to RS-485 as RTS enable or RTS block mode transfer. RS-485 can be cabled in two ways, two wire and four wire mode. Two wire mode does not allow for full duplex communication, and requires that data be transferred in only one direction at a time. For half-duplex operation, the two transmit pins should be connected to the two receive pins (Tx+ to Rx+ and Tx- to Rx-). Four wire mode allows full duplex data transfers. RS-485 does not define a connector pin-out or a set of modem control signals. RS-485 does not define a physical connector.

RS-530
RS-530 (a.k.a. EIA-530) compatibility means that RS-422 signal levels are met, and the pin-out for the DB-25 connector is specified. The EIA (Electronic Industry Association) created the RS-530 specification to detail the pin-out, and define a full set of modem control signals that can be used for regulating flow control and line status. The RS-530 specification defines two types of interface circuits, Data Terminal Equipment (DTE) and Data Circuit-Terminating Equipment (DCE). The Sealevel Systems adapter is a DTE interface.

Current Loop
This communication specification is based on the absence or presence of current, not voltage levels, over the communication lines. The logic of a Current Loop communications circuit is determined by the presence or absence of current (typically + or - 20mA). When referring to the specification, the current value is usually states (i.e. 20mA Current Loop). Current Loop is used for point to point communication and there are typically two current sources, one for transmit and one for receive. These two current sources may be located at either end of the communication line. To ensure a proper current path to ground, or loop, the cabling of two current loop communication ports will depend on the location of the current sources. Current Loop is normally good for data rates up to 19.2 Kbps. This limitation is due to the fact that the drivers and receivers are usually optically isolated circuits that are inherently slower than non-isolated equivalent circuits.

MIL-188
This communications standard comes is two varieties, MIL-188/C and MIL-188/114. Both of these interfaces are military standards that are defined by the US Department of Defense. MIL-188/114 is a differential interface and MIL-188/C is an unbalanced or single ended interface. Both MIL-188 interfaces are implemented on an RS-530 connector. MIL-188/C and MIL-188/114 have signal levels from +6 volts to -6 volts and are ideal for long distances at high speeds.

I. Background and Objective
The RS-485 communications standard was introduced in 1983 by the Electronic Industries Alliance (EIA) as a two-wire, half-duplex, multi-drop alternative to the point-to-point RS-232 interface. (Note: RS-485 can also be wired using 4-wires to enable full-duplex communication). RS-485 uses differential signaling to allow up to 32 devices to communicate peer to peer at distances up to 4000 feet. However, the EIA RS-485 specification does not stipulate the method for controlling the driver, therefore a number of alternatives have evolved.

Learn which method is most effective for minimizing the risk of communication errors in our "Eliminate the Risk of RS-485 Data Corruption" White Paper (138kb printer-friendly PDF). Download the file below.

Definition of 9-bit framing
9-bit data framing is a simple, yet effective, method of allowing many embedded devices on a multidrop network to maximize processing time. This data transfer method is designed to improve the performance of the embedded devices in these networks.

Typical 5-8 bit data framing
When using typical 5-8 bit data framing, a communication layer protocol must be used to identify the target of the message. In order for the target to ensure it gets the message, it must constantly check incoming data to see if it is a message intended for the device. This continuous data checking reduces the amount of processing time available to the embedded device.

How 9-bit framing saves time
Many embedded multidrop devices can use 9-bit data framing to significantly reduce wasted time checking network messages. 9-bit data framing uses the bit typically associated with parity error detection (see figure 1) to identify address messages. Embedded devices equipped to communicate using 9-bit data framing will ignore any serial data that does not have the address bit set unless it has previously identified an address message associated with it.

When a command needs to be sent to a device, the action is triggered by first sending an address message which all of the embedded devices will check. If the address identified is not associated with the device, it will simply go back to its normal tasks ignoring any incoming data messages. If the address identified indicates the next data messages are intended for the device, it will act on the messages appropriately.

9-bit data framing is a simple, yet effective, method of allowing many embedded devices on a multidrop network to maximize processing time.

Impact of Architecture on Performance of USB to Serial Adapters

"We were stunned at the performance difference
between brands of multiport USB to serial adapters."
Design architecture is the critical element.

Findings
There is a significant difference in performance between the "Sealevel architecture" and "industry average architecture" for USB serial adapters. Performance testing of 8-port USB serial adapters proved that the architecture determines the maximum baud rate and more importantly, the throughput of connected serial devices.

The "Sealevel architecture" uses a USB UART interface that delivers significantly faster and more reliable communications.

The "industry average architecture" 8-port USB serial adapter utilizes a USB microcontroller and a single FPGA wired to all eight serial ports. The interface between the microcontroller and FPGA creates a bottleneck because the serial devices are sharing the throughput of the microcontroller. As a result, each additional serial device added substantially reduces the speed of all eight serial ports.

Learn how multiport USB serial architecture affects your applications in our Test Report: Impact of Architecture on Performance of USB to Serial Adapters (pdf) white paper. Download the file below.

All Sealevel USB serial adapters have a dedicated USB UART design. Click on the link to see our full line of USB serial adapters.

Bluetooth Communication
Communicating via wireless connection has become commonplace in the 21st century. Cell phones, laptops, PDAs and other electronics constantly remind us of this trend. As this capability has become more widespread, so has the desire to enjoy the benefits of wireless communications in traditionally wired applications. In this application note, you will see several examples showing the benefits of accessing Sealevel SeaI/O RS-232 data acquisition modules via a Bluetooth wireless connection.

Bluetooth is an open specification for seamless wireless short-range communications to establish a Personal Area Network, or "PAN", between electronic devices. Sealevel offers a Bluetooth serial adapter (Item # BT-SD100) that interfaces to SeaI/O RS-232 data acquisition modules to allow wireless communication with any Bluetooth enabled host up to 100 meters away. An included RJ45 to DB9 cable connects the SeaI/O device with the RS-232 to Bluetooth adapter and supplies the required 5V power. Using the Sealevel universal mounting plate (Item # KT125), the Bluetooth adapter is easily mounted to the SeaI/O module using a plastic or Velcro tie wrap as shown below.

Image 1: Sealevel SeaI/O RS-232 module with Bluetooth adapter mounted to universal mounting bracket (Item# KT125)

For applications where it’s not convenient to mount the Bluetooth serial adapter to the SeaI/O module, standard DB9 RS-232 serial extension cables can be used to extend the Bluetooth adapter further away from the SeaI/O module. Since SeaI/O RS-232 modules provide power through the cable, extra cables and bulky power supplies are not needed to power the Bluetooth serial adapter.

Image 2: Sealevel SeaI/O module with remote mounted Bluetooth adapter

Once connected to the Bluetooth adapter, the SeaI/O module is easily accessed via any Bluetooth enabled host as shown in the following examples:

Bluetooth Enabled PDA Host:
A Bluetooth enabled PDA running a mobile supervisory monitoring and control program communicates with a Bluetooth enabled SeaI/O module. SeaI/O modules are a convenient way to expand your supervisory control system with optically isolated inputs, Reed and Form C relay outputs, and TTL interfaces to industry standard relay racks.

Image 3: A Bluetooth enabled PDA allows mobile supervisory monitoring and control of a Bluetooth enabled SeaI/O module

Bluetooth Enabled Laptop Host:
A Bluetooth enabled laptop running a third-party monitoring and control program interfaces two separate Bluetooth enabled SeaI/O RS232 modules. Each SeaI/O module operates as a separate slave device. Up to seven Bluetooth enabled slave devices can communicate concurrently with the host laptop.

Image 4: A laptop running third-party monitoring and control program accesses data from different SeaI/O modules via Bluetooth

Bluetooth Enabled HMI Host:
A Bluetooth enabled host HMI system is used to interface to a network of SeaI/O modules. The Bluetooth serial adapter adds a wireless Bluetooth connection to the first SeaI/O RS232 module. Up to 246 additional SeaI/O expansion modules can be added to the network via convenient RS-485 pass-through connectors on the SeaI/O module. This overcomes the traditional point-to-point limitation of RS-232 and the seven device limitation of Bluetooth.

Image 5: Host HMI system allows wireless monitoring of SeaI/O module and control of I/O via touchscreen input

Existing monitoring and control programs that use a wired RS-232 serial port will work using a wireless Bluetooth connection. Applications where Bluetooth performs well include serial cable replacement, wireless factory monitoring, control system diagnostics, and wireless vehicle monitoring, just to name a few. Call us at 864.843.4343 to discuss your specific application requirements

Hardware:
A PC or Laptop with Sealevel RS-485 serial adapters (Part# 7105, 7201, or 7205), PCMCIA serial adapter (Part# 3602) or SeaLINK USB serial adapters (Part# 2102, 2202, or 2203), along with serial cables with DB25 (Part# CA104) or DB9 (Part# CA176) connectors can be used to connect the PC to the TB04 and are available for use with any Sealevel RS-485 adapter.

Screen Capture of Active Device Search:

The Firmware Update Process
Updating the firmware on a SeaLINK Ethernet serial server takes approximately one minute to complete. This article details the steps required to update the firmware and covers two methods. Prior to SeaLINK v2.3.22 firmware, the SeaLINK Configuration Utility is required. With SeaLINK v2.3.22 firmware and later, the SeaLINK web administration page simplifies the update process.

Important!Device configuration settings will be lost after completing the firmware update. All custom configuration settings should be documented before beginning the update procedure. The SeaLINK device will need to be configured after completing the update.

Caution:When using the SeaLINK Configuration utility, the use of an uninterruptable power supply is recommended to prevent loss of power during the update. It is also recommended that the device be directly connected to the Ethernet port of the host computer using the crossover cable included with the device. In rare instances where the firmware update fails due to power loss or communication failure, it will be necessary to return the unit to Sealevel Systems for repair.

Note:With SeaLINK v2.3.22 firmware and later, updating the firmware through the web administration page is immune to communication failures. It is not necessary to use a crossover cable. However, it is still recommended to use a UPS to protect against a power failure, which would result in a return for repair situation.

Launch SeaLINK Config
The SeaLINK Configuration utility is part of the SeaLINK Software Installation package (v4.8.4+). In Microsoft Windows Vista, it is necessary to run the application as an 'Administrator'. Click on Start -> All Programs -> SeaLINK. Right-click on SeaLINK Config. In the fly-out menu, select 'Run as Administrator'.

SeaLINK Config will be used to determine the current version of the firmware installed on the SeaLINK Ethernet serial server. For older SeaLINK firmware (before v2.3.22), the SeaLINK Configuration utility can also be used to update the SeaLINK device firmware.

Click the Advanced Button
Choose the desired SeaLINK device from the list of devices detected by SeaLINK Config. Click the "Advanced" button, as shown in the image below. This will launch the web configuration utility in the default browser.

Determine Current Firmware Version
When the browser opens with the web configuration utility, the 'Summary' tab will display the current firmware version with other basic device information. Click on the 'Port Settings' and 'Administration' tabs and record any custom configuration settings for the SeaLINK device. Custom settings will be cleared during the update and returned to factory defaults.

Make note of the firmware version.

Download Updated Firmware
The latest version of the SeaLINK firmware can be downloaded from the Sealevel FTP site at the following link:

ftp://ftp.sealevel.com/pub/SOFTWARE/SEALINK/Firmware/CURRENT/

Compare the version number to the installed version and proceed if necessary. Click the file to download and save it to an accessible location such as the Desktop or My Documents folder.

Web-Based Firmware Update
Prior to downloading the firmware, you made note of the firmware version. If you see a version older than 2.3.22, you will need to use the SeaLINK Config utility to update the firmware. Skip this step and continue with the remaining steps.

If you see version 2.3.22 or newer, you can update the firmware via the web interface. Click on the 'Administration' tab. At the bottom of this page is a field, 'Flash Upgrade File'. Click the 'Browse' button and locate the firmware file you downloaded in the previous step. The SeaLINK firmware will end with '_APP.s19'. Once you have navigated to its location, click the 'Open' button. Once the field is populated with the firmware update file, click the 'Submit' button.

Depending on network speed and other factors, the firmware update will take less than one minute to complete and then the SeaLINK device will reboot. If the webpage doesn’t refresh, click on the 'Advanced' button in SeaLINK Config to launch the web configuration utility.

On the 'Summary' tab, the updated firmware version is displayed with other basic device information. Click on the 'Port Settings' and 'Administration' tabs to reconfigure the SeaLINK device using the settings you recorded prior to starting the firmware update. The firmware update and device configuration is complete.

Open Device Settings
In the SeaLINK Config window, click the 'Device Settings...' button as shown.

Click Update Firmware Button
The SeaLINK Device Settings window opens. Basic network settings are configured for the SeaLINK device in this window. Click the 'Update Firmware...' button located below the network settings options.

Click the Browse Button
Click the Browse button and locate the firmware update that you downloaded in an earlier step.

Locate the Firmware File
The SeaLINK firmware will end with '_APP.s19'.  Once you have navigated to its location, click the 'Open' button.

Click Begin Update Button
Once you have located the firmware file, click the 'Begin Update' button.

Firmware Update Complete
When the update process completes, the SeaLINK device will be fully updated. Click the Advanced button in SeaLINK Config to open the web configuration utility to verify the updated firmware version and reconfigure the SeaLINK device.

Web Configuration Utility
The web administration page for the device will appear in the default browser. On the "Summary" tab, the firmware version is displayed with other basic device information. Click on the "Port Settings" and "Administration" tabs to reconfigure the SeaLINK device using the settings you recorded prior to starting the firmware update.

Tech Support
If you experience any problems with the firmware update, contact Sealevel technical support at support@sealevel.com or call 864-843-4343 for assistance.

Hardware:
Today's Notebook PCs ship with 1 or in some cases no onboard serial ports. Sealevel USB Serial and PCMCIA Serial I/O products bypass this limitation by providing additional serial ports for all of your mobile data acquisition, automation, and control needs. Isolated USB products are also available to eliminate the effects of ground loop current and surges.

Single Port Serial Products

MultiPort Serial Products

Sealevel serial I/O devices typically include a loopback plug with each shipment that can be used to test data lines. Additional loopback plugs can be purchased for a small charge. Item number LB101 is a DB-9 loopback that is specially constructed to test data signals on RS-232 and Sealevel RS-422, RS-485 serial ports. Item number LB102 is a DB-25 loopback that is used to test RS-232 serial ports. Please contact your sales representative for more information.

If you want to test modem control signals or you need to construct your own loopback, follow the instructions below. Use the diagram appropriate to your electrical interface.

DB-9 RS-232 Loopback Connection
Connect Pins:

• 2 to 3 (Rx to Tx)
• 1 to 4 to 6 (DCD to DTR to DSR)
• 7 to 8 to 9 (RTS to CTS to RI)

Pins marked in red are the data lines, Tx and Rx, and are necessary for the loopback and BERT testing. All other pins are for modem control signal tests and are not necessary to connect unless you wish to test those signals.

DB-9 RS-422, RS-485 Loopback Connection
Connect Pins:

• 1 to 4 (Rx+ to Tx+)
• 2 to 3 (Rx- to Tx-)
• 6 to 9 (RTS+ to CTS+)
• 7 to 8 (RTS- to CTS-)

Pins marked in red are the data lines, Tx and Rx, and are necessary for the loopback and BERT testing. All other pins are for modem control signal tests and are not necessary to connect unless you wish to test those signals.

DB-25 RS-232 Loopback Connection
Connect Pins:

• 2 to 3 (Tx to Rx)
• 4 to 5 to 22 (RTS to CTS to RI)
• 6 to 8 to 20 (DSR to DCD to DTR)

Pins marked in red are the data lines, Tx and Rx, and are necessary for the loopback and BERT testing. All other pins are for modem control signal tests and are not necessary to connect unless you wish to test those signals.

DB-25 RS-422 Loopback Connection
Connect Pins:

• 12 to 24 (Rx+ to Tx+)
• 13 to 25 (Rx- to Tx-)

DB-25 RS-530 Loopback Connection
Connect Pins:

• 2 to 3 (Tx- to Rx-)
• 14 to 16 (Tx+ to Rx+)
• 5 to 4 (RTS- to CTS-)
• 13 to 19 (RTS+ to CTS+)
• 10 to 22 to 23 (DCD+ to DSR+ to DTR+)
• 6 to 8 to 20 (DCD- to DSR- to DTR-)

Pins marked in red are the data lines, Tx and Rx, and are necessary for the loopback and BERT testing. All other pins are for modem control signal tests and are not necessary to connect unless you wish to test those signals.

Hardware: A PC with Sealevel DIO-16.PCI Adapter (Part# 8002) or USB SeaLINK (Part# 8208), connected to Sealevel TB02 terminal block with CA112 cable. The TB02 and CA112 cable are available in a kit as Part# KT101.

Software Control: Reed Relay output provides contact closure to ground (common) causing the CD player to enter the selected mode of operation (Play, Pause, Stop, Forward, or Reverse).

Hardware:A PC with Sealevel PIO Adapter (Part# 8005, 8008, 8009, 8010) or USB SeaLINK (Part# 8203, 8205), connected to Sealevel TA01, Relay Rack I/O Simulator terminal block with CA167 cable. The CA167 cable from the PC to terminal block is available as an option.

Software Control: Run VBTest or VCTest to cause the LEDs to turn ON and display the switch inputs. Set the ports to input or output through the control panel. Use the TA01 to develop your application program and simulate a solid state relay rack before going live on-site.

VBTest

VCTest

Hardware: A PC or Laptop with Sealevel SeaLINK USB PIO-48 Adapter (Part# 8203) connected to an industry standard relay rack on DIN rail mounting track controlling a light pole or other industrial device. The USB cable (Part# CA179) is included with the 8203. Ribbon cables (Part# CA167) can be used to connect the 8203 to up to two standard PB24 style relay racks.

Software Control: Our included VCTest and VBtest sample applications can be used to control relay closure and input monitoring.

VBTest

VCTest

Hardware: A PC with Sealevel PLC-16.PCI (Part# 8011) board installed, connected to Sealevel TB08 terminal block. The cable from the PC to terminal block is supplied.

Visual Basic Application to turn on fan:

Hardware: A PC with Sealevel PIO-48.PCI (Part# 8005) or USB SeaPORT PIO-48 products, connected to Sealevel TB07, terminal block with CA167 cable. The cable from the PC to terminal block is available as an option.

Software Control:Run VBTEST or VCTEST to monitor switch inputs. Click on Outputs (B0) to turn LED #1 ON/OFF. Click on outputs (B1) and (B2) to turn LED #2 from Red to Green.

VBTest

VCTest

The Digital I/O Handbook
A Practical Guide to Industrial Input & Output Applications

Digital I/O Explained
Renowned technical author Jon Titus and the President and CEO of Sealevel Systems, Tom O'Hanlan, clearly explain real-world digital input/output implementation from both a hardware and software perspective. Whether you are a practicing engineer or a student, The Digital I/O Handbook will provide helpful insight you will use again and again.

• Covers a wide range of devices including optically isolated inputs, relays, and sensors
• Shows many helpful circuit diagrams and drawings
• Includes software code examples
• Presents common problems and solutions
• Detailed glossary of common industry terms

"What I like most is its mix of hardware and software. Most pages have a bit of code plus a schematic. All code snippets are in C. This is a great introduction to the tough subject of tying a computer to the real world. It's the sort of quick-start of real value to people with no experience in the field." - Jack Ganssle, The Embedded Muse, January, 2005.

You can purchase the Digital I/O Handbook for $19.95 by clicking here. The Digital I/O Handbook is FREE with any qualifying Sealevel Digital I/O product purchase.

Topics Covered

Appendix
Glossary

Appendix

Switch and Relay Configurations
When you look at the specifications for relays and mechanical switches, you'll find a variety of designations, such as DPST and 3C, associated with them. These designations describe electrical contacts and how they work. A basic on-off light switch, for example, controls one circuit (pole), and it provides a switch contact in only one position (throw). So, engineers call this a single-pole, single throw (SPST) switch. (See Figure A-1 for contact configurations.)

A single-pole switch may include an additional contact so it can turn off one device and then turn on another. This type of switch contains a set of single-pole, double-throw (SPDT) contacts. The term "double-throw" refers to a switch that can make connections in either of its two positions. Note that the two circuits in an SPDT switch always share a common signal, or pole.

Switches may include electrically separate "gangs" made up of several poles that act in unison. A double-pole, double-throw (DPDT) switch provides two independent SPDT switches operated by a single actuator. A DPDT switch can control two independent and isolated circuits.

Switches can include many poles, although for more than two poles the nomenclature uses numeric designations. So a 4PDT switch comes with four independent and isolated poles, each with two contacts. A single actuator or switch handle moves all four sets of contacts simultaneously. Keep in mind, though, that just because a switch has several poles, an application need not use them all. An SPDT switch, for example, will work just as well a SPST switch in a simple on-off circuit.

Switch nomenclature also may include designations for momentary switches; devices that either momentarily open (break) or close (make) a circuit. A pushbutton used with a doorbell operates as a normally-open switch. Pushing a normally-closed pushbutton on a lawnmower could open the ignition circuit to stop current from flowing to the sparkplug; in effect stopping the mower's gasoline engine. Momentary switches carry the designations NO for normally-open, or NC for normally-closed. Even momentary switches may come with various contact configurations, so you may encounter spring-loaded switches that offer contacts in DPDT arrangements, for example.

Electromechanical relays also provide a variety of contact configurations such as SPST, DPDT, 3PDT, and so on. But suppose you have a relay with an SPST contact. That simple designation doesn't indicate whether the switch contacts open or close when you energize the relay. You just can't tell how a relay's contacts operate without more information. Relay manufacturers use a different shorthand to designate relay contacts and the action a relay causes.

So, although relays come with standard contact configurations, such as SPDT and DPDT, the industry uses letters A, B, C, and so on, to indicate contact arrangements.

A relay with A-type contacts provides an SPST switch that closes when a circuit energizes the relay.

If you want SPST contacts to open when a circuit energizes a relay, choose one with B-type contacts. You can think of A-type contacts as normally-open (NO) and B-type contacts as normally-closed (NC).

A relay with a SPDT set of contacts-probably the most common relay contact arrangement-carries the C notation. A relay's contact diagram shows the contact arrangement and notes which contacts open or close when a circuit energizes the relay. You will find that information printed on the case of an enclosed relay or in accompanying data sheets.

Relays, like manual switches, can provide multiple sets of isolated contacts that operate simultaneously. So a relay designated 2A would provide two separate NO SPST contacts, and a 2C relay would supply the equivalent of DPDT contacts. You may find relays with other letters that designate specialized contact configurations. A set of D contacts, for example, closes one circuit before opening another, also known as a make-before-break operation.

Glossary

* - When used as a suffix on a signal name, an asterisk indicates a logic 0 causes the named action to occur. An input labeled TEST* requires a logic 0 to cause the TEST action to occur. See also: Negative Logic and /.

/ - When used as a prefix on a signal name, a forward slash indicates a logic 0 causes the named action to occur. An input labeled /RUN requires a logic 0 to cause a RUN action. See also: Negative Logic and *.

Active High - A digital signal that represents active, on, or true when its voltage is higher than the other logic state (low). Active-high signals can range from a few volts DC to as high as 24V DC, depending on the logic family or devices in use.

Active Low - A digital signal that represents active, on, or true when its voltage is lower than the other logic state (high). Active-low signals can range from digital ground to a few tenths of a volt.

Analog - A type of signal that varies continuously (lighter to darker, 4 to 20 mA, and so on), as opposed to a digital signal that can exist in only one of two possible states.

Analog Ground - The location in a system that serves as a reference ground for all analog signals. Some circuits may combine analog ground and digital ground, but most circuits separate them to reduce noise and ground currents.

AND - A logical operation in which the result is true only when all inputs are true. See: Logical AND.

AND Gate - A circuit that performs an AND operation based on the state of its inputs.

ASCII - American Standard Code for Information Interchange, an 8-bit binary code that represents characters and symbols in the Roman (English) alphabet. ASCII includes codes that controlled older communication devices, thus the CRTL key on computer keyboards.

BCD - See: Binary Coded Decimal.

Binary - A numbering system that allows for only two states, usually 1 and 0.

Binary-Coded Decimal (BCD) - The encoding of decimal numbers as four-bit binary values from 0000₂ for 0, to 1001₂ for 9. BCD uses only 10 of the 16 4-bit combinations.

Bit-Wise - An operation, usually between two bytes or words, in which corresponding bits take part in an operation.

Boolean Logic - A form of mathematics named after George Boole (1815-1864) who devised formal expressions for AND, OR, and INVERT operations.

Blocking Diode - A diode, also called an isolation diode, that stops, or blocks, current from flowing through a circuit. Typically used in a battery circuit to prevent the reverse biasing of a battery by a more positive power supply.

Buffer - An output device that operates high-current or high-voltage devices. Some manufacturers produce drivers specifically to control devices such as stepper motors or displays. See: Driver.

Buffered - A signal that has passed through a buffer. See: Buffer.

Bus - A group of related electrical signals. 1. A control bus, an address, bus, a data bus, and so on. Some buses carry specific names, such as PCI Bus and Universal Serial Bus (USB). 2. A group of conductors that distribute power.

Capacitor - An electronic component that stores a charge and provides a reserve of power in a circuit. Typically used to smooth variations in a power-supply’s output voltage, and to provide power in the event of brief power failures.

Carry Current - The amount of current a relay’s contacts can safely conduct after the contacts close.

Central Processing Unit (CPU) - The decision-making part of a computer, usually found within a computer’s microprocessor.

Chassis Ground - The ground point in a system, typically on a metal chassis, where signals connect to an earth ground. In most cases, a grounded chassis helps shield circuits from EMI and RFI, and provides a safety connection to ground. This type of ground should not carry current. See also: Analog Ground and Digital Ground.

Coil - The wire-wound electromagnetic core of a relay or solenoid. See also: Relay and Solenoid.

Complement - In logic, an operation in which a logic 1 becomes a logic 0, and vice versa. In binary numbers, the complement of 101100 = 010011.

CPU - See: Central Processing Unit.

Current - A measure of the amount of electron flow in a circuit, typically measured in amperes (A) or milliamperes (mA).

Darlington Output - A configuration of output transistors that can handle high currents. Usually found on the outputs of sensors or buffers that drive relays or solenoids.

Derate - A decrease in the rating of device characteristics, depending on operating conditions.

Digital - A system that uses discrete states to represent information.

Digital Ground - A common 0V ground reference for all digital signals. Digital ground and analog ground systems are usually wired separately to avoid introducing digital noise into the analog circuit.

Diode - An electronic component that lets current flow only in one direction.

Driver - 1. A driver circuit, or buffer, that operates high-current or high-voltage devices. 2. Driver software links application programs and specific I/O devices.

Dry Contact - 1. Metallic contacts in a relay or switch that mechanically touch to make a contact. 2. Contacts through which no current flows. See: Wet Contact.

Earth Ground - The ground point in a system that provides the lowest voltage-reference point, or ""earth."" An earth ground usually connects to a power-line ground, a ground rod, or in some cases, cold-water plumbing. An earth ground should not carry current.

Electro Magnetic Interference (EMI) - Energy induced into a circuit by radiated emissions. EMI may cause unpredictable results. See: RFI.

EMI - See: Electro Magnetic Interference.

Excitation Voltage - A voltage that powers a sensor or transducer.

Energize - To provide power to a device or circuit. Typically to power a relay coil, thus forcing it to change the state of its contacts.

Flag - 1. An electronic device, usually with two possible states, that signals an external event to a computer. 2. An internal CPU indicator that signals a condition such as register overflow or error. Sensed with software.

Flip-Flop - A bistable logic circuit that changes state due to an input event, generally a clock or pulse signal. A flip-flop remains in that state until the next input event causes it to ""flip"" or ""flop"" to its other state.

Form-A Relay - A relay that supplies normally-open (NO) SPST contacts.

Form-B Relay - A relay that supplies normally-closed (NC) SPST contacts.

Form-C Relay - A relay that supplies normally-open and normally-closed SPDT contacts.

Gate - A logic device that performs Boolean-logic operations.

Gated - A signal that is enabled, allowed to operate, or allowed to pass through a circuit depending on the state of a separate logic condition or signal.

Ground - A zero-volt reference point in a system. Provides the reference for all other voltages.

High Impedance - 1. A high resistance that reduces current flow. 2. A third state in special logic devices that "disconnects" them from a bus.

High-Side Switch - A switch that makes a connection directly to power at a higher voltage than that at the controlled load.

Impedance - Similar to resistance, an impedance represents the total opposition to the flow of current offered by a circuit. Impedance equals the vector sum of resistance and reactance, which is the complex resistance resulting from inductance and capacitance, not just pure resistance. Measured in ohms, and given the symbol, Z.

Inrush Current - A large charging current that flows into a capacitor or circuit when power is first applied.

Interposing Relay - A relay that isolates the circuit driving it, and switches a higher current or voltage than the driving circuit could provide. See: Relay.

Inverter - A logic device that complements the logic state of its input. See: Complement.

I/O - Input/output, as in I/O port. See: Port.

Isolation - A condition that separates circuits so no current can flow between them. Special devices such as opto-couplers provide a signal path between two circuits, but without current flow between them.

Latch - A logic circuit that takes a ""snapshot"" of information and saves it. Latches operate using an edge-triggered or a level-triggered control signal.

LED - See: Light-Emitting Diode.

Light-Emitting Diode (LED) - A diode that emits light when current passes through it (forward biased). LEDs provide white light as well as most colors. LEDs usually require an external current-limiting resistor.

Logical AND - A Boolean-logic operation that produces a true output only when all the function or circuit inputs exist in the true state.

Logical OR - A Boolean-logic operation that produces a false output only when all the function or circuit inputs exist in the false state.

Logic Ground - A ground-reference point in a circuit for all logic signals. Usually kept separate from other grounds in a system due to noise concerns.

Low Impedance - A low-resistance circuit that usually requires high current to drive it, as opposed to a high-impedance circuit.

Low-Side Switch - A switch that makes a connection directly to ground.

Mask Byte - A combination of 1’s and 0’s used in a bit-wise logical operation to set or clear individual bits. Masks can exist as any integer value, such as byte, word, long word, and so on.

NAND Gate - A circuit that performs a NOT-AND operation based on the state of its inputs. This gate performs an AND operation and inverts (NOTs) its output.

Negative Logic - A notation that indicates a logic 0 represents the active state for a signal.

Non-Buffered - An unbuffered signal that should not drive more than a few inputs within its logic family. See: Buffered.

NOR Gate - A circuit that performs a NOT-OR operation based on the state of its inputs. This gate performs an OR operation and inverts (NOTs) its output.

Normally-Closed (NC) - Relay or switch contacts that normally form a complete low-resistance path for current flow. In an unenergized relay, a set of closed contacts.

Normally-Open (NO) - Relay or switch contacts that normally do not make contact. In an unenergized relay, a set of open contacts.

NOT - The equivalent of an inversion operation, usually applied as part of another logic element or operation. See: Inverter.

NPN - A type of transistor often used as an on-off switch in electronic devices. An NPN switch usually sinks current from a higher potential through a device to ground.

Open Collector - A logic device or sensor that provides an output transistor with an unconnected collector. When turned on, this transistor sinks current to ground, but it cannot source any current. An open-collector output usually serves as a switch to ground.

Optical Coupler - See: Opto-Coupler.

Optical Isolator - See: Opto-Coupler.

Optical Isolation - The use of a light path to transfer a signal from a transmitter, usually a light emitting diode (LED), to a receiver, usually a phototransistor. This technique provides electrical isolation as a signal passes from one circuit to another.

Opto-Coupler - A device that uses light emissions to cause an isolated output stage to turn on. This device allows detection and sensing of potentially dangerous or high voltage signals, while providing isolation and protection to the circuitry sensing them.

Opto-Isolator - See: Opto-Coupler.

OR - A logical operation or circuit in which the result is false only when all inputs are false. See: Logical OR.

OR Gate - A circuit that performs an OR operation based on the state of its inputs.

Overload Protection - The capability to protect a circuit when current exceeds a predetermined value. Devices such as fuses or circuit breakers automatically disconnect a load when they sense an overcurrent.

PNP - A type of transistor often used as an on-off switch in electronic devices. A PNP switch usually sources current from a positive supply to a device at a lower potential.

Port - A collection of signals that go to or from a computer for the input or output of information. For example, an 8-bit input port or a serial port.

Positive Logic - A notation that indicates a logic 1 represents the active state for a signal.

Pull-Down Resistor - A resistor used to pull a logic input ""down"" to the low state, or logic-0 state, thus preventing a disconnected input from floating into an undetermined state.

Pull-Up Resistor - A resistor used to pull a logic input ""up"" to the high state, or logic-1 state, thus preventing a disconnected input from floating into an undetermined state.

Radio Frequency Interference (RFI) - Unwanted high-frequency signals, often generated by switching circuits, power supplies, computer cables, and oscillators. RFI may interfere with the proper operation of other circuits.

Reed Relay - A small relay comprising two magnetic contacts within a sealed glass envelope. When energized, a coil around the envelope moves the contacts to make a low-resistance connection. See: Relay.

Relay - A device that opens or closes a circuit under control of a separate and isolated circuit. A mechanical relay uses a coil to actuate mechanical contacts. A solid state relay uses electronic devices to open or close circuit paths. Both types of relays isolate the controlling circuit from the circuit the relay controls.

Resistance - The total amount of opposition to current in a circuit. Resistance carries the units of ohms and the Greek symbol omega, Ω. Resistance values may have units of kilohms, kΩ or megohms MΩ. See: Resistor.

Resistance Temperature Detector - A stable, linear temperature detector that provides a varying resistance in direct proportion to temperature changes.

Resistor - A device that opposes or limits current flow. Usually noted in schematic diagrams as R. See: Resistance.

RFI - See: Radio Frequency Interference.

RTD - See: Resistance Temperature Detector.

Sensor - A device that monitors or measures phenomena such as temperature, pressure, light intensity, weight, conductivity, and so on. Sensors may provide digital or analog output proportional to the phenomenon measured.

Single-Pole Double-Throw (SPDT) - A three-terminal switch or relay in which one central terminal connects to either one of the other two terminals. This type of switch can alternately connect a signal to one of two devices.

Single-Pole Single-Throw (SPST) - A two-terminal switch or relay that can open or close one circuit.

Sink - The ability to allow current to flow through the circuit, usually to ground.

Snubber - A circuit that suppresses inductive ""kickback"" that may result when inductive loads switch off. Unless snubbed, the kickback voltage can harm the device that drives the load. See: Suppression Diode.

Solenoid - An electrical coil equipped with a magnetic core. Energizing the coil moves the core. Removing the current lets the solenoid core return to its normal position. Solenoids move levers, open valves, and so on.

Solid State Relay (SSR) - A solid state circuit that employs devices such as opto-couplers, transistors, and triacs to perform the function of a mechanical relay. See: Relay.

Source - The ability to provide current flow.

SPDT - See: Single-Pole Double-Throw.

SPST - See: Single-Pole Single-Throw.

SSR - See: Solid State Relay.

Supply Current - The total current that a circuit requires from a power supply.

Suppression Diode - A reverse-biased diode placed across a relay or solenoid coil. When the coil loses power, the diode provides a short circuit that quickly dissipates energy stored in the coil.

Surge Current - A high charging current that flows into a power supply filter capacitor or similar circuit as the power is first turned on. Similar to inrush current.

Surge Suppressor - A circuit that limits the effects of power surges. Devices such as metal-oxide varistors (MOVs), zener diodes, and fuses provide this function.

Switch - An electronic or mechanical device that can connect one signal to a series of connections. Switches ideally have zero impedance when closed and infinite impedance when open.

Thermocouple - A temperature transducer made of two dissimilar metals welded together at one point to form a junction that, whenheated in a complete circuit, generates a small voltage proportional to the junction temperature.

Three State - An output from a logic device that can exist in one of three states; logic 0, logic 1, or a high-impedance (disconnected) state. This latter state allows multiple outputs to connect to one signal, effectively providing a "bus" that many signals can share. Three-state devices will provide an output-enable signal that either connects logic signals to the device’s outputs, or places the outputs in a high-impedance state. (National Semiconductor owns the trademark, "tristate™," although the term finds common use among designers.)

Transistor-Transistor-Logic (TTL) - The type of circuit used in the popular 7400 logic-device families.

Transparent Latch - A latch that passes signals from its inputs to its outputs as long as its Enable signal remains active—usually logic 1. When the Enable signal changes to its inactive state—usually a logic 0—the latch closes and then the outputs remain as they were when the Enable signal changed from logic 1 to logic 0. In effect, this IC acts like a small memory.

Triac - A semiconductor switch that can control devices powered by AC current.

Truth Table - A table that shows all possible input and output conditions for a logic element such as a gate or flip-flop. This table may show binary states as well as clock and signal transitions.

TTL - See: Transistor-Transistor-Logic.

VA - See: Volt-Ampere.

VCC - The symbol for the positive supply voltage in a circuit. Also noted as V_CC.

Volt - The unit of potential difference or electromotive force, abbreviated V. One volt represents the potential difference needed to produce one ampere of current through a resistance of one ohm.

Voltage - The term used to designate electrical potential that causes current to flow.

Volt-Ampere - The unit of apparent power in an AC circuit containing capacitive or inductive reactance. The apparent power is the product of source voltage and current. Abbreviated VA.

Watt - The unit of electrical power required to do work at the rate of one joule per second. One watt of power is expended when one ampere of direct current flows through a resistance of one ohm. Abbreviated W.

Wet Contact - 1. Mercury-wetted contacts in sealed reed relays. When the contacts meet, the surface tension of the mercury draws the contacts together and forms a low-resistance path for low-level signals. In effect, the small amount of mercury ensures low-resistance contacts for low-level signals that don’t clean the contacts. 2. Contacts through which current flows. See: Dry Contact.

Zero-Crossing Detector - A circuit that detects when an AC voltage signal has reached zero volts. Switching a circuit at this time reduces inrush currents and minimizes any EMI or RFI produced during switching.

For more information
We hope you found the Appendix & Glossary useful. To go back to the Main Page, click here.

You can purchase the complete Digital I/O Handbook for only $19.95 by clicking here. The Digital I/O Handbook is FREE with any qualifying Sealevel Digital I/O product purchase. You can find a listing of all Sealevel Digital I/O products by clicking here.

The Digital I/O Handbook
A Practical Guide to Industrial Input & Output Applications

Digital I/O Explained
Renowned technical author Jon Titus and the President and CEO of Sealevel Systems, Tom O'Hanlan, clearly explain real-world digital input/output implementation from both a hardware and software perspective. Whether you are a practicing engineer or a student, The Digital I/O Handbook will provide helpful insight you will use again and again.

• Covers a wide range of devices including optically isolated inputs, relays, and sensors
• Shows many helpful circuit diagrams and drawings
• Includes software code examples
• Presents common problems and solutions
• Detailed glossary of common industry terms

"What I like most is its mix of hardware and software. Most pages have a bit of code plus a schematic. All code snippets are in C. This is a great introduction to the tough subject of tying a computer to the real world. It's the sort of quick-start of real value to people with no experience in the field." - Jack Ganssle, The Embedded Muse, January, 2005.

You can purchase the Digital I/O Handbook for $19.95 by clicking here. The Digital I/O Handbook is FREE with any qualifying Sealevel Digital I/O product purchase.

Chapter 4 - Sensor Interfacing

In Chapter 3 you learned how to set up a computer to acquire data from electronic devices. In this chapter, you'll learn more about connecting, or interfacing, several types of sensor outputs to a computer.

Topics Covered

• Example 1: Thermal switch
• Example 2: Level switch
• Example 3: Hall-effect proximity switch
• Example 4: Photoelectric sensor
• Example 5: Shaft encoder
• Example 6: Output more than 8 bits

Example 1. Thermal switch
A thermal switch such as a Klixon Series 6786 from Texas Instruments (www.ti.com) provides a snap-action metallic disk that responds to temperature changes. At a specified temperature, the disk either makes or breaks an electrical contact, depending on the model. Buyers can specify an operating temperature and whether the thermal switch provides a normally-open (NO) or normally-closed (NC) contact. When the switch reaches the specified temperature, an NC switch will open and an NO switch will close.

Assume you have a NO switch that operates at 40°C (104°F). When the contacts close, you want a computer to start a process, say, turn on a fan. Because the switch supplies uncommitted contacts — no connections to power or ground — you can connect the switch to a computer in several ways, as shown in Figure 4-1a-d. In this type of application, it’s unlikely the circuit needs to debounce the switch.

Figure 4-1
A simple on-off SPST switch can connect to a computer interface either directly or through an optical isolator. The direct connection should limit the distance from the switch and the interface to a few inches.

If the switch forms part of the computer’s circuitry, perhaps as part of a controller that keeps the computer cool, the circuit probably can use a power supply in common with the computer, as shown in Figures 4-1a, -1c and -1d. (Note the use of a Schmitt trigger in one circuit.) This device "cleans up" the edges of the logic transitions produced by the switch to provide a "clean" TTL-compatible signal. If the thermal switch exists at some distance from the computer, consider using an optical isolator, as shown in Figure 4-1b.

Switches with SPST contacts exist in many other devices, such as magnetic sensors, float switches, and air-flow sensors. The circuits developed in this example should work well with them all. Most temperature-sensitive switches exhibit an effect called hysteresis. In a typical switch, the contacts close at, say, 40°C (104°F), but they don’t reopen until the temperature decreases to 35°C (95°F), as shown in Figure 4-2. Thus, the thermal switch will not rapidly open or close as the temperature hovers around 40°C. The temperature must decrease to 35°C to reset the switch. This built-in effect keeps a computer from trying to regulate a temperature within a degree or two of its setpoint. Even home heating and cooling thermostats provide a few degrees of hysteresis. If they didn’t the heat and air conditioner would go on and off in short cycles.

Figure 4-2
Many sensors exhibit some form of hysteresis. In this example, a thermal switch closes its contacts at 40°C. As the switch cools, the contacts open only when the switch reaches 35°C. Hysteresis may have a narrower range, depending on the sensor and its application.

Example 2. Level switch
A capacitive level detector provides a SPDT switch as its output indicator. The specification sheet provides information about how the detector works and it shows the switch’s operation when the detector senses a change in capacitance near the probe. The detector operates an internal relay that provided a set of SPDT contacts, so you can treat the sensor’s outputs just as you would the thermal switch shown in Figure 4-1.

Because the switch offers SPDT contacts, you decide to add a cross-coupled NAND gate, as shown previously in Figure 3-4, to debounce the switch. In theory, that circuit will work, but the wires that connect the SPDT switch to the cross-coupled NAND gates may have to run for a considerable distance. Unfortunately, most TTL signals should not run more than about 10 inches from one device to another! So, we recommend you use one of the optically isolated circuits shown in Figure 4-1.

If you sense a level using a float switch, a capacitance switch, or similar sensor, remember that liquids can slosh around in containers and that pumping and draining may cause liquid levels to fluctuate. Without some built-in hysteresis, a level switch can turn on and off when it detects every slight disturbance in liquid level. Sensor specification sheets should specify the hysteresis range for an on-off sensor.

If a sensor does not include some form of hysteresis, software can often "even out" a switch signal to determine whether or not its contacts are closed. When the software detects a switch closure (or opening), instead of immediately taking action, the software can wait briefly and test the switch several more times with a short delay between tests. This type of software filtering or "debouncing" proves helpful when you can’t find a suitable sensor with hysteresis, or if you can’t easily debounce a switch with electronics.

The following program listing shows how software could test a switch several times in a subroutine. In this example, the software must detect a logic 0 from the switch (at bit D2), seven times in a row, with a 10-millisecond delay between tests. The logic-0 state indicates a switch-closed condition. A subroutine (not shown) provides a 10-millisecond delay between tests of the switch’s state.

Dim	max_count	As Byte
Dim	switch_count	As Byte
Dim	switch_mask	As Byte
Dim	switch_port	As Integer

max_count	= 7
switch_mask	= &H02	'00000010
switch_port	= 135

'Switch-debounce subroutine
Sub Switch_check
switch_count		= 0	'Initialize counter
For loop = 1 to max_count
	If (inportb(switch_port) AND switch_mask = 0)
		Then
		(switch_count = switch_count + 1)
	End If
milli_sec_delay 10			'Millisecond-delay subroutine call
Next
If max_count = switch_count
	Then		'Switch closed, so do this...
End If
End Sub

Each time through the test loop, the software increments a switch_count variable if it detects a logic-0 from the switch. If at the end of seven tests, the switch_count equals the number of passes through the loop, max_count, the software assumes the switch really exists in its closed state.

As an alternate approach, the software could test for, say, five proper states out of seven tries in the loop. To do so, substitute the following four statements for the last four in the listing above:

If (max_count - 2) <= switch_count			'OK if at least
			'5 of 7 tests
	Then 'Switch closed, so do this...		'detect a switch
			'closure
End If
End Sub

Before we leave this example, two notes about programming:

1. Most switches will stop bouncing in under 10 milliseconds, so your application software may not need to go to the extremes shown above. We included the code as a teaching example. Some switches, though, can bounce for as long as 1/6th or 1/5th of a second! (Refs. 1 and 2.)
2. If you need to debounce several switches in software, you can set up a subroutine for each one. Or, you can set up a general switch-test subroutine, procedure, or function that can accept arguments (values) transferred to it. These values include max_count, switch_mask, and switch_port for each switch you need to test. This approach makes it easy to change your parameters without having to rewrite the switch-test code for each switch.

Example 3. Hall-effect proximity switch
Semiconductor Hall-effect switches respond to changes in magnetic fields, so designers use them to detect the proximity of ferro-magnetic materials. These solid state switches act rapidly and can detect thousands of changes per second, so they find use in applications that count revolutions on a mechanical shaft, detect the presence of a magnet, and so on.

Several Hall-effect switches from Phoenix America (www.phoenixamerica.com) and Allegro Microsystems (www.allegromicro.com) provide "open collector" outputs. How can this output connect to an input port? This type of output comes from an NPN transistor that connects a circuit to ground, and it will readily provide a signal to an input port.

Many Hall-effect switches require an external power source. For these switches, you can choose to connect the ground from that power source to your computer system ground and directly connect the switch as shown in Figure 4-3a. That circuit will work when you can make a short-distance connection between your computer system and the switch. We recommend using the optically isolated circuit shown in Figure 4-3b because it keeps the Hall-effect switch’s power isolated from the computer. If you use an optical isolator in your interface circuit, the Hall-effect switch’s external power supply can provide current to drive the LED.

Figure 4-3
A Hall-effect switch with an NPN output transistor (open collector) sinks current to ground. The switch can use either a direct connection or an optically isolated connection to an input port.

Example 4. Photoelectric sensor
Commercial photoelectric sensor modules, such as those in the CX Series from Automation Direct (www.automationdirect.com), detect the presence or absence of an object in a light beam. Some detectors provide a built-in light source and rely on reflections from an object. Other sensors require a remote light source and detect objects that interrupt a light beam. The sensor manufacturer offers models with four output options: NPN NO, NPN NC, PNP NO, or PNP NC. How can you interface these sensors to a computer?

First, the NC and NO refer to the output as either normally closed or normally open, respectively. So, think in terms of a normally-open or normally-closed switch.

Second, the PNP and NPN refer to the type of transistor on the output. An NPN transistor sinks current to ground while a PNP transistor sources current from a higher potential. Treat these outputs as you would any other NPN or PNP output. The CX Series photoelectric sensors provide a power source, so use an optical isolator to separate the sensor circuits from the computer circuits as shown in Figure 4-4.

Figure 4-4
Some photoelectric sensors offer a choice of PNP or NPN outputs. This schematic diagram shows how to connect either output type to an input port through an optical isolator.

Example 5: Shaft encoder
Incremental shaft encoders produce a fixed number of pulses or "counts" per revolution of a central shaft. Manufacturers offer a range of encoder types that offer various counts/revolution (CPR)—from 35 CPR to several thousand CPR. The phase of the output pulses establishes the direction of the shaft’s rotation and its relative position. A 1000 CPR encoder that produces a series of 212 pulses lets you determine the shaft has moved 360° * 212/1000, or 76° from its previous position.

This type of incremental encoder does not provide an absolute position of, say, 95°. It only provides an indication of the distance moved from the previous position. (By measuring the rate at which pulses occur, you can determine the rotational speed of the shaft.)

An incremental encoder produces two square-wave outputs that an external counter can accumulate to determine the relative change in a shaft’s position. The lead-lag phase relationship between the two square waves indicates whether a shaft rotates clockwise or counterclockwise, as shown in Figure 4-5. A D-type flip-flop can use the out-of-phase signals to produce a "rotation" signal. The circuit shown includes two 74HCT4538 monostable circuits that combine to produce a short pulse for each transition on the A or B square wave.

Additional circuitry, perhaps a 10- or 12-bit up-down counter (not shown), can use these pulses and the flip-flop’s direction signal to keep track of the shaft’s position. Microcontrollers that can connect directly to an incremental encoder can handle the counting through software.

Figure 4-5
The phase relationship between square waves produced by a shaft encoder lets a flip-flop IC determine rotation direction. A pair of monostable ICs produces a pulse for each transition on the A or B output from the encoder.

Some incremental encoders include an optional index output that produces a single short pulse at one point in a complete rotation. Circuitry can use this pulse to reset a count or increment a separate "turns" counter. US Digital (Vancouver, WA; www.usdigital.com) provides a variety of encoders and interface ICs that can simplify the design of interface circuits. We won’t go into more detail on how rotary encoders operate.

Assume for the moment you have purchased or designed an external counter circuit for an incremental encoder with 1024 counts/revolution. That means each complete rotation of the encoder’s shaft will produce a 10-bit binary count: 2¹⁰ = 1024. So far, input ports have acquired data in 8-bit bytes, so how can a computer input 10 bits from a counter? You can split the 10 bits into an 8-bit byte at one input port, and route the remaining two bits to another input port, as shown in Figure 4-6. (We have shown the unused bits at input port 202 connecter to logic 1; +5V through a pull-up resistor.)

Figure 4-6
Two input ports let software gather data from a device that puts out more than eight bits. If the data can change rapidly, this arrangement can lead to errors.

This arrangement may run into problems because it requires two input operations, separated by a finite time. To illustrate the potential problem, assume a split of a 10-bit value 0011110101₂ (245) into 00, the two most-significant bits, and 11110101₂, the eight least-significant bits. Several counts, each incremented by 1 appear as:

00	11110101	(245)
00	11110110	(246)
00	11110111	(247)
00	11111000	(248)
00	11111001	(249)
and so on...

Assume the software first acquires the least-significant eight bits, D7—D0 at input-port 203 and then acquires the two most-significant bits, D9—D8 at input-port 202.

Given a count of 00 11110101₂ at the encoder’s circuit, you would expect to find those bits in the computer after the two input-port commands execute. As long as the data remain constant between the two input commands, you’ll see the expected result.

But suppose a mechanism moves the shaft between the time the software acquires bits D7—D0 and when it acquires bits D9—D8. The movement adds 20 pulses to the count, which goes from 00 11110101₂ (245) to 01 00001001₂ (265). That change represents a rotation of only about 7°. The steps below show what happens in this case:

1. The computer acquires the eight LSBs: 00 11110101₂
2. A mechanism rotates the shaft and the counter increments its count by 20 to produce a new count of: 01 00001001₂
3. The computer now acquires the two MSBs: 01 00001001₂

Now, when the computer combines the binary values, it turns into:
01 11110101₂, which is WRONG!

The motion of the shaft between the two input operations caused the problem. Granted, this condition won’t occur frequently, but without some way to prevent it, you will never know when it has occurred!

Any circuit that must transfer more than eight bits at a time, from a single source such as a counter, must first latch the entire n-bit value into a set of latches or D flip- flops as shown in Figure 4-7. The 74LS374 inputs provide D flip-flops that latch the data (controlled by the CLK inputs). The 74LS374 ICs also provide three-state outputs (controlled by the /OC inputs). So the same ICs provide the latch and three-state logic functions. Some devices, such as digital meters, may provide latched outputs, but they may lack three-state outputs.

Figure 4-7
The 74LS374 ICs in this circuit first latch all 10 bits and then transfer a byte at a time to a computer. Latching the bits provides stable data for the software to acquire.

To start an acquisition, the computer first latches the entire 10-bit value from the counter by strobing both 74LS374 ICs with the OUT231 pulse. In this case, the output-port instruction such as outportb(231, n) simply generates the latch-control pulse. Although the 8-bit value for n goes out on the data bus, no device actually uses it. So it doesn’t matter what value you use for n. Software often uses output-port commands to create a pulse for use in an interface circuit.

After latching the entire 10-bit value simultaneously, the computer can gather the bits from input ports 202 and 203 and reassemble them with software. Any changes of the counter’s outputs will not affect the data saved in the latch. After acquiring the two bytes from input ports 202 and 203, how does the software recombine them into a value an application program can use?

The software below shows the needed operations. The software needs two bytes to save input-port data and an integer value (16 bits) to save the final 10-bit count:

Dim	counter_value	As Integer
Dim	MS_bits	As Byte
Dim	LS_bits	As Byte
outportb(231, 0)		'Latch all bits
MS_bits = inportb(202)		'Get bits D9-D8
LS_bits = inportb(203)		'Get bits D7-D0
MS_bits = MS_bits AND &H03
counter_value = LS_bits + (256 * MS_bits)

The last statement multiplies the decimal value of bits D9 and D8 by 256 to compute the value they represent at the counter. Then the statement adds them to the decimal value of bits D7—D0. The result, counter_value, will have a value of 0 to 1023. Remember, the computer "sees" bits D9 and D8 at positions D1 and D0 at input port 202. The input port and the computer have no knowledge of the "weights" of these bits as they come from the 10-bit counter circuit. You must track their value and reconstruct it using software.

But why does the sequence of commands include a bit-wise AND with a mask of 00000011₂? That bit-wise AND operation ensures bits D7—D2 in the MS_bits byte get set to zero so they will not get used in calculation of the 10-bit count value. The circuit in Figure 4-7 forced the unused bits at input port 202 to logic 1, so the bit-wise AND clears them to logic 0. Couldn’t the circuit have simply forced the bits to logic 0 (ground) to save the trouble of using a bit-wise AND? Of course. But we would have included the logic operation in any case. Never assume you know the state of unused bits. Always play it safe and mask off any unused or unneeded bits.

At some point, an engineer might decide to use some of the "unused" bits at port 202 to detect flags or input switch data. Masking out those bits while writing the software ensures you won’t have difficulties later due to later unplanned changes in circuits.

Example 6: Output more than 8 bits
Simultaneously transferring more than eight bits to an external device may cause timing problems much like those experienced in the incremental-encoder example. Although two output ports handle 16 bits, software can update only one port at a time. So, if an output device requires that an interface circuit apply more than eight bits simultaneously, first set up an n-bit latch that acquires all n bits at one time. Then use as many output ports as necessary to "feed" data to that latch, one byte at a time.

Figure 4-8 shows a circuit set up as an interface for a 12-bit device. The circuit uses a 74LS374 D-flip-flop IC for output port 003 and another 74LS374 IC as output port 004. The pair of 74LS374 ICs on the right side of the circuit forms an intermediate 16-bit latch that will simultaneously transfer all data from the output ports to the 12-bit device. (The circuit does not use four of the output bits. Never tie unused ports to +5V or ground!)

Figure 4-8
A double-buffered interface circuit lets two 8-bit output ports produce data for simultaneous transfer to a 12-bit device. Many output devices come with built-in double buffers.

To perform a transfer, software first sends individual bytes to ports 003 and 004 and then simultaneously transfers all the data to the 12-bit device by using an outportb command for port 005. Keep in mind the needed outportb(005, n) command serves only to generate the OUT005 pulse. Although the command transfers byte n onto the computer’s data bus, no device uses it, so the value of n is immaterial.

This technique often goes by the name "double buffering," and many manufacturers provide the necessary double-buffer circuits in their devices. The Analog Devices (Norwood, MA; www.analog.com) AD5341 12-bit digital-to-analog converter (ADC), for example, includes double buffering in the chip so 8-bit microprocessors and microcontrollers can use the IC without external circuitry.

Before software can send more than eight bits to an external device, it must "split" the data into the various 8-bit bytes, and math and bit-wise-logic operations help. (We’ll assume a 16-bit value, but the techniques apply to higher bit counts, too.)

For this example, start with the 16-bit value 525 or 0000001000001101₂, which software must split into two bytes: 00000010₂ and 00001101₂ for transfer to the output ports. To get the least-significant byte, use the modulus operation: mod in Visual Basic and % in C/C++. This operation performs modulus division and produces the remainder of a division. So, when software performs the operation:

525 Mod 256

the result yields a remainder of 13 (00001101₂), the lower byte. Then, software can divide the entire value 525 by 256 and force the result of that operation into an integer value to strip off the remainder:

525 / 256 = 2.05078 and then Int(525 / 256) yields 2

to yield the upper byte 00000010₂.

Logical operations also can split a 16-bit value into two bytes. Again start with the value 525 or 0000001000001101₂. Perform a bit-wise AND with 255 and the lower byte "falls through" the mask:

0000001000001101

0000000011111111

0000000000001101

Then move the remaining value into an 8-bit integer to obtain the lower byte: 00001101

Next, use a mask on the upper eight bits:

0000001000001101

1111111100000000

0000001000000000

and divide by 256, which in effect shifts all the bits to the right by eight positions:

0000000000000010

Move the result into an 8-bit integer value to obtain 00000010₂.

1. Ensure its math operations perform the mod and int functions.
2. Ensure you can use 16-bit unsigned integer value.

References

1. Ganssle, Jack G., "The Secret Life of Switches," Embedded Systems Programming, April 2004. pp. 61—64. (www.embedded.com)
2. Ganssle, Jack G., "Solving Switch Bounce Problems," Embedded Systems Programming, May 2004. pp. 45—64.

For more information
We hope you found the Chapter 4 informative. To go back to the Main Page, click here.

You can purchase the complete Digital I/O Handbook for only $19.95 by clicking here. The Digital I/O Handbook is FREE with any qualifying Sealevel Digital I/O product purchase. You can find a listing of all Sealevel Digital I/O products by clicking here.