Depending on the purpose, sometimes also one or more handshake lines are crosslinked. With a null modem connection the transmit and receive lines are crosslinked. The RS-232 standard is asymmetric as to the definitions of the two ends of the communications link, assuming that one end is a DTE and the other is a DCE, e.g. It is also used to serially connect a computer to a printer, since both are DTE, and is known as a Printer Cable. The name stems from the historical use of RS-232 cables to connect two teleprinter devices or two modems in order to communicate with one another null modem communication refers to using a crossed-over RS-232 cable to connect the teleprinters directly to one another without the modems. It simply reverses some of the pins so that the output on one computer is being sent to the input of another. Some of us have fond memories of using a cross-over cable to play multiplayer games before the internet was a thing.Null modem is a communication method to directly connect two DTEs ( computer, terminal, printer, etc.) using an RS-232 serial cable. However, a crossover cable can be used to connect two devices directly, without the need for a router in the middle. The router takes all the bits being sent out by the computers and relays them onto the other devices on the network, or out to the wider internet. In a Ethernet networking environment - like in a family home with multiple PCs that are wired - the computers must all connect to a central router.

If you're interested in learning more about networking in general, we have a complete Beginner's Guide to Home Networks you should take a look at first. However, we've never described how to make a cross-over cable. The article may be old, but it's still as relevant today as ever. We've showed you before how to make your own straight-through Ethernet cabling.

Crossover cable pinout download