Here is the
common PC serial port pinout
and what the role of each pin is as specified by the
RS232 standard.
D-Type-9 Pin No. (MALE)
1 5
-------------
\ o o o o o /
\ o o o o /
---------
6 9
D-Type-25 Pin No. (MALE)
1 13
-----------------------------
\ o o o o o o o o o o o o o /
\ o o o o o o o o o o o o /
------------------------
14 25
25 Pin No. 9 Pin No. Abbreviation| Full Name | FUNCTION |
Pin 8 Pin 1 CD Carrier Detect | When the modem detects a "Carrier" from another modem at the other end of the line. |
Pin 3 Pin 2 RD Receive Data | Serial Data Input (RXD) |
Pin 2 Pin 3 TD Transmit Data | Serial Data Output (TXD) |
Pin 20 Pin 4 DTR Data Terminal Ready | Opposite to DSR. The UART is ready to communicate. |
Pin 7 Pin 5 SG Signal Ground |
Pin 6 Pin 6 DSR Data Set Ready | Tells the UART that the modem is ready to establish a link. |
Pin 4 Pin 7 RTS Request To Send | Flow Control. Informs the Modem that the UART is ready to exchange data. |
Pin 5 Pin 8 CTS Clear To Send | Flow Control. Indicates that the Modem is ready to exchange data. |
Pin 22 Pin 9 RI Ring Indicator | Indicates a ringing signal |