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RS-232 Cable Connections
Commonly used DB9 / DB25 cable connections for EIA/TIA-232 and V.24 Asynchronous Interfaces.
DB9 DB25 NAME SYMBOL FUNCTION
1 8 Data Carrier Detect DCD Handshake from DCE
2* 3 Receive Data RxD Data from DCE
3* 2 Transmit Data TxD Data from DTE
4 20 Data Terminal Ready DTR Handshake from DTE
5* 7 Signal Ground GND Ground/Return
6 6 Data Set Ready DSR Handshake from DCE
7 4 Request to Send RTS Handshake from DTE
8 5 Clear to Send CTS Handshake from DCE
9 22 Ring Indicator RI Handshake from DCE
* Only pins used by API Multi-drop.
NOTE: Generally Asynchronous host equipment only requires the TxD, RxD and GND signals as
indicated by the asterisk (*). If your host system requires certain handshake signals, you must wire
back those signals to the corresponding handshake response lines. Wire host connectors as shown in
the table below:
Host DB25 to M-drop DB9
HOST M-DROP
Signal
Host DB9 to M-drop DB9
HOST M-DROP
2 3 TxD/RxD 2 3
3 2 RxD/TxD 3 2
7 5 GND 5 5
4 to 5 n/c RTS/CTS 7 to 8 n/c
6 to 20 n/c DSR/DTR 4 to 6 n/c
8 n/c DCD 1 n/c
22 n/c RI 9 n/c