X.21 Cabling

Use these diagrams as a reference when building or purchasing X.21 cables. See Tips for Building and Purchasing Cables for cable length and quality concerns.

DB-15 Pin Number	Signal	DB-15 Male Connector
2	TxD (A)
9	TxD (B)
3	Control (A)
10	Control (B)
4	RxD (A)
11	RxD (B) (B)
5	Indicator (A)
12	Indicator (B)
6	Signal Element Timing In (A)
7	Signal Element Timing Out (A)
13	Signal Element Timing In (B)
14	Signal Element Timing Out (B)
8	Signal Ground
1 and shell	CGND