Null Modem Cable
DB9 (D-Sub 9-pin) Female to
DB9 (D-Sub 9-pin) Male
CB-NM-9DBF-9DBM-xx

Null Modem serial cables allows two DTE (computer, terminal, printer, etc...) or DCE (i.e. modems ...) devices to communicate with no conflict in data transmission. The transmit and receive signals are crossed to ensure proper data transmission. Cables in male-to-female configurations are typically used as serial printer cables, while female-to-female versions are typically connecting two PC serial ports.

With a null modem connection the transmit and receive lines are crosslinked. Depending on the purpose, sometimes also one or more handshake lines are crosslinked. Several wiring layouts are in use because the null modem connection is not covered by a standard.