Serial (RS232) null modem cable (DB9-DB25). Pinout and signals for building a serial (RS232) nullmodem cable

Use this cable between two DTE devices (for instance two computers).

DB9 pin D-SUB female to PC1
DB9 pin D-SUB female to PC1
DB25 pin D-SUB female to PC2
DB25 pin D-SUB female to PC2

DB9 DB25
Receive Data
2
2
Transmit Data
Transmit Data
3
3
Receive Data
Data Terminal Ready
4
6+8
Data Set Ready + Carrier Detect
System Ground
5
7
System Ground
Data Set Ready + Carrier Detect
6+1
20
Data Terminal Ready
Request to Send
7
5
Clear to Send
Clear to Send
8
4
Request to Send
Note: DSR & CD are jumpered to fool the programs to think that they are online.

Our software allows you monitor, log, debug and test any your RS232 or COM ports.