Enterasys SBUQHS/QHB, User Manual

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Interface Signals
80-14001000-03 9–1
9 Interface Signals
9.1 X.21 Operation
X.21 uses a balanced form of signalling which requires two circuits for
each interface signal.
The User connectors are all female 15 way 'D' type, Link connectors (for
backup modules) are male 15 way 'D' type.
The pin assignments are as follows:
Pin No. Circuit No. Signal Name
1 Ground Chassis Earth
8 G Signal Ground / Chassis Earth
2 Ta Transmit Data A
9 Tb Transmit Data B
3 Ca Control A
10 Cb Control B
4 Ra Receive Data A
11 Rb Receive Data B
5 Ia Indicate A
12 Ib Indicate B
6 Sa Signal Timing A
13 Sb Signal Timing B