USB to Synchronous Radio Adapter


The U.S. military uses several manufacturers for tactical radios that provide data communications and situational awareness on the battlefield, making it difficult to achieve interoperability from one radio to another. To solve this problem, Sealevel partnered with the Defense Information Systems Agency (DISA) to develop the ACC-188, a non-proprietary, interoperable USB synchronous interface that works seamlessly with DISA’s PDA-184 tactical data communications software application. The ACC-188 adapter and PDA-184 software enable PC-compatible computers (mainly mobile devices) to connect to tactical radios to transmit and receive IP data such as email, text messages, GPS maps, images, coordinates, and other communications. Sealevel functions as the prime contractor for the Department of Defense for the ACC-188 and directly managed the project from initial design through manufacturing.

Application Requirements

  • USB Interface to Synchronous RS-232 (MIL-STD-188-184 Waveform)
  • Data Rates to 76K bps
  • Hot Swappable
  • Low Power (<0.3W)
  • Shielded to Protect from RF Interference
  • Small and Lightweight for Easy Portability
  • Resistant to Liquid, Dust, and Dirt

The Sealevel Solution

Sealevel designed a data cable with an integrated USB to synchronous serial converter that provided the fast throughput, low power, and small, rugged, mechanical design required for connecting a tactical radio to a computer’s USB port. Based on a Field Programmable Gate Array (FPGA), the ACC-188 requires less than 0.3W of power, which is critical for field use with battery-powered devices. The electronics are encapsulated in an aluminum chassis with rubber overmold to reduce susceptibility to EMI and make the device as rugged as possible while maintaining a small size. Additionally, the mechanical design provides robust shielding to protect from the high-levels of electromagnetic interference (EMI) generated by the radios, eliminating a major flaw associated with other competing designs.

Key Design Challenge

Fast, Reliable USB to Synchronous Data Conversion
Sealevel’s electrical team created an innovative design to implement the conversion from the tactical radio’s high-speed synchronous serial connection to a standard USB interface compatible with any PC. The heart of the design is an 8-bit microcontroller with integrated USB port and an FPGA. The FPGA includes a 256-byte Receive FIFO for receiving high-speed serial data from the radio. Using the clock signal supplied by the radio, the incoming data is clocked into the FIFO and stored until the microprocessor organizes the data into byte format and transfers the formatted data to the PC via USB packets. Similarly, on message transmission, the USB packets are sent to the FPGA’s Transmit FIFO and subsequently clocked out one bit at a time to the radio.