Specifications

SDM-100A Satellite Modem Theory of Operation
Rev. 0 4–17
Fault indicators are also provided on TTL open collector drivers on the RS-422
connector.
• The TTL MOD fault indicates one of the following:
 MODULATOR fault
 COMMON EQUIPMENT fault
• The TTL DEMOD fault indicates one of the following:
 DEMOD fault
 COMMON EQUIPMENT fault
4.4.1.1 Connector Pinouts
The RS-422 interface is provided on a 37-pin female D connector accessible from the
rear panel of the modem. Screw locks are provided for mechanical security of the mating
connector.
Signal Function Name Pin #
Send Data SD-A 4
SD-B 22
Send Timing ST-A 5
ST-B 23
Receive Data RD-A 6
RD-B 24
Request To Send RS-A 7 (See note below)
RS-B 25 (See note below)
Receiver Timing RT-A 8
RT-B 26
Clear To Send CS-A 9 (See note below)
CS-B 27 (See note below)
Data Mode DM-A 11
DM-B 29
Receiver Ready RR-A 13
RR-B 31
Terminal Timing TT-A 17
TT-B 35
Master Clock (Input) MC-A 16
MC-B 34
Demod Fault — 21
Mod Fault — 3
Signal Ground SG 1, 19, 20, 37
Note: The Request to Send (RTS) line is hard-wired to the Clear to Send (CTS) line
by JP11, pins 5 and 6, on the Demodulator/M&C card (AS/4973), since the modem
does not support polled operation.