Campbell Scientific NL100 Network Link Interface - 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