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

This cable should be used for DTE to DCE (for instance computer to modem) connections without hardware handshaking.

DB9 pin D-SUB female to the computer
DB9 pin D-SUB female to the computer
DB25 pin D-SUB male to the modem
DB25 pin D-SUB male to the modem

  Female Male Direction
Shield Ground
1
Transmit Data
3
2
—»
Receive Data
2
3
«—
System Ground
5
7
Jumper these:
Request to Send
7
«—
Clear to Send
8
«—
Data Set Ready
6
«—
Carrier Detect
1
«—
Data Terminal Ready
4
—»
Request to Send
4
—»
Clear to Send
5
«—
Data Set Ready
6
«—
Carrier Detect
8
«—
Data Terminal Ready
20
—»