Specifications

Asynchronous Overhead Channel Unit SDM-650B Satellite Modem
F–2 Rev. 5
F.1 Functional Description of ASYNC Overhead Channel Unit
The ASYNC overhead interface module consists of three subassemblies:
• Connector board (AS/1328)
• Terrestrial interface (AS/1311)
• Data processor board (AS/1289)
The connector board provides the physical interface utilizing a 50-pin D connector. The
terrestrial interface contains all circuitry required for G.703, RS-422, MIL-STD-188, and
V.35 type interfaces for synchronous data. The terrestrial interface also contains circuitry
for RS-232-C and RS-485 type interfaces for ASYNC data.
The data processor contains all circuitry required for:
• Multiplexing the synchronous and ASYNC data streams
• Data rate synthesizers
• Optional plesiochronous buffer
Refer to Figure F-1 for a block diagram of the ASYNC overhead interface.