Interface Adapter User's Guide

Appendix B Null Modem Cable Requirements 31
RS-449 Null Modem Cable
TABLE B-1 and TABLE B-2 list the signals and names for RS-499 and X.21 circuits.
TABLE B-1 RS-449 Signals
Circuit Name Direction
TxD Transmit Data To DCE
RxD Receive Data From DCE
TxC Transmit Clock To DCE
TxCI Transmit Clock In From DCE
RxC Receive Clock From DCE
RTS Request to Send To DCE
CTS Clear to Send From DCE
DCD Data Carrier Detect From DCE
DTR Data Terminal Ready To DCE
DSR Data Set Ready From DCE
SG Signal Ground
TABLE B-2 X.21 Signals
Circuit Name Direction
G Signal Ground
T Transmit To DCE
R Receive From DCE
C Control To DCE
I Indication From DCE
S Signal Element Timing From DCE
B Byte Timing From DCE