null modem

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null modem

(communications, hardware)
A cable, especially an EIA-232 cable, for connecting serial ports on two computers directly, rather than via modems. Since, according to the specification, both computers should transmit on pin three of their EIA-232 connectors and receive on pin two, a null modem cable needs to connect one computer's pin two to the other's pin three and vice versa. It also needs to have male connectors at both ends (again, according to the specification).
References in periodicals archive ?
This product can be used with a hardware null-modem (COM port - RS232) cable or Network for TCP/IP.
Smart dongles are connected to host terminals using a three-wire null-modem serial RS-232 interface, which is used for transferring data, command and control, and firmware updating.
All you need is a serial cable, and in some cases a null-modem adapter (or cable), to connect the instrument to the existing serial ports (com ports) on your PC.
In between these two you'll also need a 9-pin null-modem adapter and a gender changer.
Each PC is then cabled to the control server using RS232 null-modem or RJ45 cabling (not provided).