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256-KBPS LINE DRIVER (V.35, RS-530, OR X.21)
Table 4-5. Pinout of the RackNest 2/14’s DB25 connector when
ME445C-X21 is installed.
SIGNAL ITU-TSS LEAD DB25 DA15
NAME (ABBREV.) CIRCUIT TYPE (RACK- (NORM.
NEST) X.21)
PIN* PIN
Shield (n/a) 101 1 1
Ground (G) 102 7 8
a.k.a. Signal Ground (SGND)
Transmit (T) 103 A 2 2
B14 9
Receive (R) 104 A 3 4
B16 11
Control (C) 105 A 4 3
a.k.a. Request to Send (RTS) B 19 10
Indication (I) 109 A 8 5
a.k.a. Carrier Detect (CD) 10 12
RS-530: Transmitter Signal Element 113 A 24 7†
Timing (DTE Source) (TSETT)† B 11 14†
Signal Timing (S) 114 A 15 6
B12 13
*This pinout follows the TIA RS-530 standard.
†Standard X.21 does not support an external clock, and specifies that DA15 Pins 7
and 14 should be used for the Byte Timing (B) A and B signals. Because Byte
Timing is hardly ever used, but an external clock is often necessary for today’s
data communication, many Black Box devices are designed to this modified
specification in which the RS-530 external-clock signal replaces Byte Timing.