How Does a USB to Serial Adapter Work?

By Rebecca O'Brien

Few older devices use USB connectors, but most modern computers use this type of port to transfer data. By using a USB to serial adapter, you can continue to use your older serial-enabled device through your new computer's USB port. These cables are also referred to as USB to DB9 or or USB to RS-232 cables and are sold at electronics specialty stores.

USB to serial adapters are cables that convert the data sent by a serial-enabled device for use by a USB port. The serial end has a DB9 connector, which plugs into the serial device. The USB connector plugs into the computer's USB port or a connected USB hub. The data that are transmitted by the serial device are sent directly to the USB port, where it is passed to software to interpret it.

Each adapter cable is sold with a driver CD, which must be installed before the cable is used. The software creates a virtual serial port. As data are transmitted through the USB port, they come in as a serial signal. The USB port can recognize the information, but can't do anything with it, since it is not a USB signal. The USB port sends the data to the installed software, which searches for the serial data and interprets them for use by other computer programs. When information is sent to the serial device, it performs the same operation in reverse.

Not all serial devices can be used with USB to serial adapters, and some computers do not support the software. Before purchasing a USB to serial adapter, make sure your computer meets the requirements for the adapter's software and try to contact the company to determine if your device is supported.