RS-232 and other serial ports and interfaces  > DEC pinouts
Found on the DEC Multia and DEC UDB (Universal Desktop Box). It contains two Serial ports on one connector. The 1st port is located on the normal pins, and the 2nd port is located on some "spare" pins.
Pin Port Name Dir Description
1   n/c   Not connected
2 1 TXD --> Transmit Data (RS232)
3 1 RXD <-- Receive Data
4 1 RTS --> Ready To Send
5 1 CTS <-- Clear To Send
6 1 DSR <-- Data Set Ready
7 1+2 GND - Ground
8 1 DCD <-- Data Carrier Detect
9   n/c   Not connected
10   n/c   Not connected
11 2 DTR --> Data Terminal Ready
12 2 DCD <-- Data Carrier Detect
13 2 CTS <-- Clear To Send
14 2 TXD --> Transmit Data
15   n/c   Not connected
16 2 RXD <-- Receive Data
17   n/c   Not connected
18   n/c   Not connected
19 2 RTS --> Ready To Send
20 1 DTR --> Data Terminal Ready
21   n/c   Not connected
22 1 RI <-- Ring Indicator
23 2 DSR <-- Data Set Ready
24   n/c   Not connected
25 2 RI <-- Ring Indicator

Note: Direction is DTE (Computer) relative DCE (Modem).

25 pin D-SUB male connector layout
25 pin D-SUB male connector
at the computer
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Source(s) of this and additional information: Tommy"s pinout Collection by Tommy Johnson; Digital UDB Information by Eric Smith, from Hardware Book
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