Appendix A Cable Pin Assignments & Signals 27
Interface Signals

Functional descriptions of the RS-449 interface signals are provided in TABLEA-2.

TABLEA-2 RS-449 Interface Signals
RS-449Pin
No. SignalName Function
1 Shield Ground Enables tandem sections of shielded cable to retaincontinuity
throughthe connector.
19 Signal Ground (SG) Directlyconnects the DTE circuit ground to the DCE circuit
ground,providing a path for DTE and DCE signal commons.
4/22 TransmitData (TxD) Usedby the DTE to pass binary data to the DCE for
transmission over the communications channel.
6/24 Receive Data (RxD) Used by the DCE to pass binary data received from the
communications channel to the DTE.
5/23 TransmitClock in (TxCI) Enables the DCE to transmit signal element timing to the DTE.
Thisenables the DTE Transmit Data signal on circuit TxD to be
in synchronizationwith On/Offtransitions on this lead.
8/26 Receive Clock (RxC) Transitionson this lead enables the DTE to time data received
over circuitRxD.
17/35 TransmitClock (TxC) Enablesthe DTE to provide transmit timing information to the
DCE so that the DTE can synchronizewith data arriving over
the TxD lead.
7/25 Request to Send (RTS) Usedby the DTE to advise the DCE it is ready to transmit data.
9/27 Clear to Send (CTS) Used by the DCE to advise the DTE that the DCE is ready to
send data over the communications channel.
11/29 Data Set Ready (DSR) Used to advise the DTE of the Ready status on the DCE. In
most cases, this signal simply implies the unit is poweredon.
12/30 Data TerminalReady (DTR) Used by the DTE to advise the DCE it is readyto transmit or
receive.
13/31 Data Carrier Detect (DCD) TheDCE uses this lead to advise the DTE that an incoming
signal on the communications channel is present.When first
initializedthis signal is an indication to the DTE to expect data
momentarily.