Serial (RS232) modem cable (DB25-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.

D25 pin D-SUB female to the PC
DB25 pin D-SUB female to the PC
DB25 pin D-SUB male to the modem
DB25 pin D-SUB male to the modem

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