Comtech EF Data SDM-650B - Manual (Page 77)

SDM-650B Satellite Modem Configuration
Rev. 5 3–35
3.2.5.3 Multiplexer
The data processor, AS/1289, forms the bottom of the 2-board module. This board
contains the data multiplexer and demultiplexer.
The synchronous data stream is multiplexed with a 1/15 overhead channel, and the
resultant information is interfaced to the modulator/coder section of the modem.
The input clock is normally the recovered clock from the terrestrial interface board
(SCTE), but the modem reference clock can be used by selecting INT Clock.
The 1/15 overhead channel is composed of:
• Framing signals
• Flags
• Spare bit positions
• Asynchronous data stream
The maximum asynchronous data rate is limited to 1.875% of the synchronous data rate.
3.2.5.4 Demultiplexer
Receive data and clock from the demodulator/decoder is input to the demultiplexer. The
demultiplexer synchronizes to the frame pattern and separates the synchronous and
asynchronous data. Synchronization is indicated by the DEMUX lock LED on the front
edge of the board.
The synchronous data is dejittered and interfaced either to the optional plesiochronous
buffer or to the terrestrial interface board.