A null modem cable is an RS-232 serial communication cable used to connect two devices directly without a modem. It was widely used for updating firmware on older equipment, including satellite receivers, industrial devices, and various types of legacy hardware. Today, the demand for null modem cables has significantly decreased, making them more difficult to find. As a result, this type of cable is gradually becoming obsolete.
This article shows the pinout of an RS-232 null modem cable. To make one yourself, you will need two RS-232 connectors and a three-core cable approximately 1 to 1.5 meters long. After purchasing the necessary components, solder the wires according to the diagram below.
If your computer does not have an RS-232 serial port, you can use a USB-to-RS-232 adapter.