Most Sealevel serial adapters use the serial drivers built into the Linux kernel. For USB and UART-based serial adapters, the Linux drivers may need additional information in order to provide access to the Sealevel serial device. For SeaLINK Ethernet serial servers, Sealevel offers a dedicated Linux driver.

• To configure UART-based serial adapters, please read How to configure UART-based serial adapters in Linux.
• To configure USB serial adapters, please read How to configure USB serial adapters in Linux.
• For Ethernet serial servers, please download the Sealevel SeaLINK software driver for Linux.

Microsoft Windows maintains the configuration (enumeration) information for every USB device that has ever been connected, unless you explicitly uninstalled the device before unplugging it. When a USB device is not physically connected to the computer, Windows does not normally display the device in Windows Device Manager. These USB devices are called “non-present” or “phantom” devices.

Windows Device Manager can be used to uninstall or change the properties of non-present USB devices after a session-specific variable has been set. This variable can be set in a command window in Windows 2000 and later. These commands must be “Run as administrator” in Windows 7, Vista or later.

• set DevMgr_show_NonPresent_Devices=1
• devmgmt.msc

These commands set the variable and open Windows Device Manager. In the Device Manager window, click the View menu and set the 'Show hidden devices' option.

Non-present devices appear with a ghosted icon. Right-click on the non-present device and select 'Uninstall' in the fly-out menu.

Sealevel SeaLINK Ethernet serial servers support a 2-byte format to marshal 9-bit serial data between the host computer and the serial server. The least significant bit of the first byte is the 9^th bit of the serial frame and the second byte is the first 8 data bits of the serial frame. SeaLINK Ethernet serial servers also support 9-bit serial tunneling.

SeaLINK Ethernet serial servers use RFC-2217, the Telnet COM port control protocol, to transmit modem control signals in serial tunneling mode. Since SeaLINK Ethernet serial servers are DTE devices, they follow standard null-modem conventions to tunnel output modem control signals. This is done in two parts as explained below.

Setting the output modem control signals on the remote serial server

The remote SeaLINK serial server sets output modem control signals on the output serial port when it receives the matching RFC-2217 command:

• Set DTR ON
• Set DTR OFF
• Set CTS ON
• Set CTS OFF

Receiving input modem control signals on the local serial server

When input modem control signals are set on the input serial port, the local SeaLINK Ethernet serial server will send the RFC-2217 commands to set DTR or CTS as follows:

• When a SeaLINK device sees either the DSR or DCD input is ON, it sends the RFC-2217 command to set DTR ON.
• When a SeaLINK device sees both the DSR and DCD inputs are OFF, it sends the RFC-2217 command to set DTR OFF.
• When a SeaLINK device sees the CTS input is ON, it sends the RFC-2217 command to set RTS ON.
• When a SeaLINK device sees the CTS input is OFF, it sends the RFC-2217 command to set RTS OFF.

The extra data is non-serial Telnet command messages such as COM port settings and modem control signals. SeaLINK devices communicate using the RFC-2217 Telnet Com Port Control protocol so they also send control sequences and certain bytes in a Telnet compliant manner.

Every Telnet control sequence begins with the "Interrupt As Command" (IAC) byte, which has the decimal value 255. Serial data is sent with the IAC value (decimal 255) repeated as a two-byte (escaped) sequence. The receiving device interprets that two-byte sequence as a single (unescaped) serial data byte with decimal value 255 instead of a Telnet control sequence.

To optimize a SeaLINK Ethernet serial server for lower latency, disable Nagle’s algorithm on both the SeaLINK device and virtual COM port driver. SeaLINK devices and drivers use Nagle’s algorithm, also referred to as “nagling”, to increase serial data throughput while reducing network traffic.

By default, SeaLINK Ethernet serial servers use Nagle's algorithm to reduce network traffic and increase serial data throughput, with the side effect of increasing latency. Both SeaLINK devices and the virtual COM port driver have settings to disable Nagle's algorithm, also referred to as "nagling". To reduce latency, disable Nagle's algorithm in both the SeaLINK device and driver.

Sealevel USB serial adapters are supported by the SeaCOM driver, which includes a latency timer with a default setting of 16 msec. Decreasing this value reduces the amount of time a USB device buffers data before completing a write to the host computer, which increases the CPU overhead of the driver. A full USB device buffer is sent immediately without waiting for the timer to expire. Decreasing the latency timer can improve performance related issues and should reduce the overall latency of read cycles.

To access the latency timer, navigate to Windows Device Manager; expand the ‘Ports’ section and right-click on the USB to serial adapter listed. Click ‘Properties’ to open the device properties window. Click the ‘Ports Settings’ tab followed by the ‘Advanced…’ button. The ‘Latency Timer (msec)’ drop box is located in the ‘BM Options’ group on the left side of the window.

To avoid potential data loss, we do not recommend setting the latency timer below 4 msec. The latency timer does not affect the transmission of data from the host computer to the USB device.

You are describing the "crazy mouse" syndrome, a common condition when Microsoft Windows receives NMEA 0183 data from a serial GPS device. The condition occurs when the GPS data is misinterpreted as mouse data by the Windows serial enumerator and will cause unwanted mouse cursor activity. It is most commonly encountered when connecting a serial GPS device to any USB to serial adapter. It is easily remedied in Windows Device Manager by disabling the Windows serial enumerator for the COM port connected to the GPS.

For more information, read the How to fix "crazy mouse" syndrome with USB serial adapters article.

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.

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.

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 most convenient method is to use a Sealevel Interface Converter to convert the electrical interface from RS-232 to RS-422 or RS-485. Use one of our interface converters at each end, with standard twisted pair cable in between, and you can communicate with your RS-232 device up to 4,000 feet away from your computer. Sealevel Interface Converters handle the electrical interface conversion in hardware so it is completely transparent to your software application.

You may also consider using a Sealevel Ethernet Serial Server. The RS-232 ports on the serial server are recognized as virtual COM ports by your computer. This allows you to communicate with your RS-232 device, anywhere on your Ethernet network, as though it were connected directly to your computer.

The optional 16950 UART provides the following benefits:

• 8x more baud rates due to 1/8th clock prescalar
• 128-byte FIFO buffer
• 9-bit protocol support
• Isochronous mode

Contact your sales representative for a quote.

RS-232, RS-422, and RS-485 are serial communication methods for computers and devices. There are two articles in the Resource Center section of the Sealevel website that address these standards:

• Overview of Serial Communication Standards
• Choosing Serial I/O for Control Networks

For Windows 95/98/ME/2000/XP/Vista, use Device Manager to uninstall the product prior to removing it from the computer or unplugging it, as in the case with USB serial. This ensures that when the product is reinstalled, the system will see it as a new piece of hardware.

Since many Sealevel devices install as "Parent/Child" devices, the trick is making sure to uninstall the Parent device. Our PCI serial and ISA serial cards will typically have the Parent device installed under the "Multiport Serial" category. Uninstalling this device will remove both the Parent and Child COM port devices. For USB serial devices, the Parent device will be installed in the "Universal Serial Bus" category. If it is a single channel USB serial device the Parent device will be either a SeaLINK or SeaPORT entry. For multi-port USB serial devices, uninstall all occurrences of "Generic USB Hub".

For Windows NT, the system should be shut down and the product removed. Allow Windows NT to boot without the product. The device driver will detect that the hardware is no longer in the system and will remove the now invalid device. Shut the system down and reinstall the hardware. Upon boot up the device should be reinstalled.

• Make sure connections are clean and secure and thumbscrews are tightened
• If running long distances, choose a low capacitance cable
• Avoid running communication cables near AC power lines, fluorescent lights, motors, transformers or any devices with a strong magnetic field
• High-quality shielded cables are included with certain Sealevel serial devices and are also available as accessories.

Using an optically isolated serial device alleviates the problem caused by ground loops, floating grounds, or small surges. Sealevel offers a variety of optically isolated serial products including the following interfaces:

USB
2103 – 1-Port RS-232 DB25
2104 – 1-Port RS-422/485 DB25
2113 – 1-Port RS-232/422/485 DB9 (DIN Rail or Table Mount)
2213 – 2-Port RS-232/422/485 DB9 (DIN Rail or Table Mount)

Ethernet
4103 – 1-Port RS-232/422/485 DB9 (with Opto-isolated input and Reed relay)

PCI
7108 – 1-Port RS-232/422/485 DB25 (Low Profile and Full Height available)
7203 – 2-Port RS-232/422/485 DB9 (Full Height)

Compact PCI
7903 – 2-Port RS-232/422/485 DB9 (3U)

Interface Converters
1103 – 1-Port RS-232 to RS-422/485 DB25
1105 – 1-Port RS-232 to RS-422/485 Screw Terminals (DIN Rail Mount)

ISA
3189 – 2-Port RS-422/485 DB9

There are known issues with the USB driver built into Windows XP SP1 (Service Pack 1) that affect suspend, hibernation, and restarting. This issue potentially affects all USB devices and is not specific to those manufactured by Sealevel.

Microsoft released Hotfix 822603 to address this problem. If you are running Windows XP SP1, visit the link for information on downloading and installing the patch. If you are running Windows XP SP2 (Service Pack 2) or greater, you are already using the updated driver and do not need to install this patch.

Only the data pins (TX and RX) are necessary for a loop back test. Unless you need to test the modem control signals (RTS, CTS, DCD, DTR, DSR, and RI) there is no need to connect them. Please refer to your manual for the correct pin assignments for your serial device.

For RS-232 serial devices:

• Connect TX to RX
• Connect RTS to CTS to RI
• Connect DTR to DCD to DSR

For RS-422, RS-485 serial devices:

• Connect TX+ to RX+ and TX- to RX-
• Connect RTS+ to CTS+ and RTS- to CTS-

For RS-530 serial devices:

• Connect TX+ to RX+ and TX- to RX-
• Connect RTS+ to CTS+ and RTS- to CTS-
• Connect DTR+ to DCD+ to DSR+ and DTR- to DCD- to DSR-

A good economical solution for field wiring is to use CAT5 or CAT6 twisted pair cable. Connect each twisted pair to the same set of signal pins – TX+/TX- would be one pair of conductors, RX+/RX- another pair of conductors, and GND a third pair of conductors. This helps to cancel out noise or voltage differences that are induced or radiated into untwisted cables. To easily terminate twisted pair field wiring, use the Sealevel TBRJ45 terminal block with an RJ45 connector to screw terminals.

Sealevel offers several accessories for interfacing many serial connections. The universal D-Shell Converter Kit (Item# DB101) includes DB9 and DB25 Male and Female connectors, D-sub hoods and wires. The DB101 makes it easy to build a custom gender adapter or convert a legacy pin out.

Sealevel offers a D-Shell Modular Adapter Kit (Item# DB102) that makes it easy to connect DB9 and DB25 serial connectors together using standard CAT5 cables. Preconfigured modular adapters are available for various pin outs. Other cable, adapter, and converter options are available on the Sealevel accessories webpage.

PortMon for Microsoft Windows is a very useful tool. This utility monitors all serial port activity, shows how an application uses a port, and identifies problems with system or application configurations. You can find other helpful utility programs on the Microsoft® Sysinternals website.

The simplest method is to use a null modem cable (Item# CA213), which reverses the transmit and receive signals between the serial devices. This method only works for short distances.

For distances over 50 feet, a better method is to use a pair of Sealevel Ethernet Serial Servers and configure them for "serial tunneling". This allows asynchronous serial devices to communicate over an Ethernet network eliminating costly upgrades to application programs or serial devices. Barcode scanners, RFID readers, scales, sensors, and other serial devices can be located remotely on the network, yet communicate with a host serial device as though they were directly connected to a local serial port.

Sealevel Ethernet Serial Servers support serial tunneling and can be configured via a simple web interface.

No. Standard DB25 to DB9 adapters and cables are made to convert an RS-232 DB25 pin out to an RS-232 DB9 pin out. As such, they do not pass the correct signals through for RS-422 or RS-485. Please see the following question regarding using standard RS-530 cables or visit the cable accessories page for cabling options.

We maintain serial programming samples with source code on our FTP site:

ftp.sealevel.com/pub/SOFTWARE/SEACOM/source samples/

Examples of programming samples include: a simple terminal program; a program to toggle modem control signals; and a Win32 API program to send and receive test data.

Practically, it depends on your application and environment.

The RS-232 standard specifies transmitting data up to 50 feet at 9600 bits per second (bps).

It is always a good idea to terminate any un-used signal lines. Floating signals can generate interrupts and drastically degrade system performance. The Sealevel SeaCOM serial driver provides a means of suppressing modem control interrupts. The driver features can be located in the Microsoft Windows Device Manager. If you are not using the Sealevel SeaCOM serial driver, or are using a different operating system, terminate each modem control line by connecting it to its complement:

• Connect CTS to RTS
• Connect DCD to DTR to DSR

Yes. The Sealevel SeaCOM serial driver fully supports interrupt sharing. There are however a couple of points to mention.

All Sealevel PCI serial cards fully support interrupt sharing on Windows 95/98/ME/2000/XP and Vista operating systems. In order for interrupt sharing to work properly, all devices connected to an interrupt must support sharing. If any device or its associated driver is connected to an interrupt and does not support interrupt sharing, then all other devices attempting to share that interrupt will fail.

Sealevel four port (Part# 3405 and 3440) and eight port (Part# 3420) ISA serial boards have special onboard circuitry to support interrupt sharing. The ISA interrupt sharing is supported on these select boards and only with the Sealevel SeaCOM serial driver.

The GPS modified boards are designed to work primarily with the Rockwell Collins GPS receiver with a data rate of 76.8 Kbps. The modification is necessary because 76.8 Kbps is not a standard baud rate. To get 76.8 Kbps select 115.2 Kbps as your data rate in the SeaCOM driver. This will result in an actual data rate of 76.8 Kbps. For a more detailed description of the two GPS modifications, download the GPS instructions, below. If you would like to order a GPS modified board, contact your sales representative for a quote.

By connecting the ground wire, you avoid potential communication problems. Differential serial communications such as RS-422 and RS-485 use the ground as a reference. When there is no ground, the reference is basically floating. Communication failures can result if the floating reference causes the data line voltage to exceed the common mode range of the transmitter/receiver. When devices are on different power circuits there is a high probability of ground differences that can lead to communication failures or device damage.

The SeaCOM serial driver looks exactly like the Windows driver to your application. SeaCOM uses the same API and calls as the Microsoft driver. However, SeaCOM provides many additional features not provided by the Microsoft serial driver such as:

• Auto RS-485 RTS control
• Support for advanced UARTS
• Interrupt sharing in Windows 95/98 for ISA Products
• Suppression of modem control interrupts
• Advanced configuration options

Additional features and information can be found on the SeaCOM software webpage.

There are only a few cases where you would want to change a COM number assignment. Your application only works at COM1 through COM4 and the Sealevel serial device you just installed comes in at COM5 or higher. Or, you just installed a multiport serial card and the COM numbers were not assigned consecutively. The ability to change the COM number assignments depends on which Windows operating system you are using. To complicate things further, a previously installed USB or PCMCIA device may not even be physically in the system when you attempt to make the change. Sealevel highly recommends using the installed COM numbers if at all possible. However, Sealevel offers a few solutions for changing COM number assignments depending on which operating system you are using.

Older versions of Windows (95/98/ME) do not provide a way to change the COM number assignments. The Sealevel SeaCOM serial driver automatically installs the Port Manager utility and it can be found in the Start menu in the SeaCOM folder. Port Manager provides a method to change the COM number assignments in these versions of Windows.

Windows NT does not provide a way to change COM number assignments either. The Sealevel SeaCOM serial drivers installs the Advanced Ports utility in the Control Panel. Advanced Ports is used to change COM assignments in Windows NT.

In Windows 2000/XP, you can change the COM number assignment using Device Manager. In Device Manager, select the "Ports COM and LPT" category, select the COM port you want to change, click on the "Port Settings" tab, then click the "Advanced" button. A new dialog window appears with a drop down box that allows you to change the COM number assignment.

Serial tunneling works by pairing two Sealevel Ethernet Serial Servers (located on the same subnet) together by configuring each others’ IP address. When one serial server receives serial data, it converts the data to network packets and transmits it to the other serial server. The receiving serial server strips the network information, converts it back to serial data and then transmits it to the receiving serial device. Other than the initial configuration, no computer is required for the devices to communicate and bidirectional communications is fully supported.

Yes. An RS-530 to RS-422/485 interface cable will be required to match up the signal pin outs of the interfaces. Use the CA176 cable to connect the DB25 connector of an RS-530 device to the DB9 connector of a Sealevel RS-422/485 serial port.

Sealevel products are tested with many popular software programs. The 3rd Party Software Support page has a list of these programs with links to application notes that will help your get your Sealevel product working in your choice of application.

If you are using a software program not listed on the 3rd Party Software page, please contact Technical Support for assistance.