D-sub 9 Connector Pinout

Pinout and diagram of DE9 connector (DB9 connector), commonly used for serial ports (RS-232).

Pin SIG. Signal Name DTE (PC)
1 DCD Data Carrier Detect in
2 RXD Receive Data in
3 TXD Transmit Data out
4 DTR Data Terminal Ready out
5 GND Signal Ground -
6 DSR Data Set Ready in
7 RTS Request to Send out
8 CTS Clear to Send in
9 RI Ring Indicator in

The DTE (PC) has the male connector (shown below), and the DCE (peripheral) has the female.

RS-232 Maximum Cable Length

The maximum cable length for RS-232 is 50ft, but in practise depends on baud rate, cable specific capacitance and ambient noise. The table below contains some rules-of-thumb from experiments done by Texas Instruments years ago.

Baud rateMaximum range / cable length
1920050ft
9600500ft
48001000ft
24003000ft

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