What is null-modem?

A null-modem is a cable that is used to connect two serial devices directly to each other without the use of a modem or computer. It is also sometimes referred to as a crossover cable or a serial extension cable. This type of cable is commonly used to transfer data between two computers or various other devices such as switches, routers, and serial printers.

The term "null-modem" refers to the fact that the modem signals that would normally be transmitted between two devices are nullified or eliminated when using this cable. The cable is wired in such a way that the transmit pin of one device is connected to the receive pin of the other device and vice versa. This creates a direct channel of communication between the two devices.

Null-modem cables are often used in situations where one device does not have a network card or the ability to connect to a network, or where a direct connection between two devices is desired for security reasons. These cables are available in different lengths and configurations depending on the devices being connected.