Black Box ME444AE-530-R3, ME444AE-R3, ME445C-X.21, ME445C-35, ME444A-R3, ME445C-530 manual DB25 DA15

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
		B	14	9
Receive (R)	104	A	3	4
		B	16	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
		B	12	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.

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