Null Modem

What Does Null Modem Mean?

A null modem is a specially designed cable that allows a “head-to-head” connection between two nearby serial devices (computers) through their communication ports (RS-232). Having a length limitation of up to 30 feet, it is most commonly used to connect PCs within the same room for gaming and other purposes such as sending and receiving files.

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A null modem is also known as a crossover cable.

Techopedia Explains Null Modem

A null modem uses a modem protocol with Tx (transmit) and Rx (receive) lines only suitable for serial connections. An RS-232 serial communication interface is the standard communication channel through the data terminal equipment (DTE) — usually a personal computer — and data communications equipment (DCE), or the modem. Sending and receiving is done by separate lines, each of which has a function that enables the communication. A DTE sends data on the line which is the receiving line for the DCE. Sometimes in the absence of a DCE interface, the null modem makes the DTE interface of a PC look like a DCE interface in order to facilitate communication.

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Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.