Appendix b. null-modem cable – Campbell Scientific NL100 Network Link Interface User Manual
Page 33
Appendix B. Null-Modem Cable
A null-modem cable allows communication between two similar devices. It is
sometimes called a crossover cable, because the transmit and receive lines are
crossed so that the two devices can communicate. An RS-232 null modem
cable usually also crosses other handshaking lines.
An RS-232 null-modem cable can be purchased at a local computer store. The
pin-outs for this cable are provided below.
Carrier Detect
1
⇔ 4
Data Terminal Ready
Transmit Data
2
⇔ 3
Receive Data
Receive Data
3
⇔ 2
Transmit Data
Data Terminal Ready
4
⇔ 1, 6 Carrier Detect, Data Set Ready
Signal Ground
5
⇔ 5
Signal Ground
Data Set Ready
6
⇔ 4
Data Terminal Ready
Request to Send
7
⇔ 8
Clear to Send
Clear to Send
8
⇔ 7
Request to Send
Not Used
9
9
Not Used
B-1