USB adapter

A USB adapter is a type of which is used for converting USB data signals to and from other communications standards. Commonly, USB adaptors are used to convert USB data to standard serial port data and vice versa.

Most commonly the USB data signals are converted to either RS232, RS485, RS422 or TTL serial data. The older serial RS423 protocol is rarely used any more, so USB to RS423 adapters are less common.

USB to serial RS232 adapters are often used with consumer, commercial and industrial applications and USB to serial RS485/RS422 adapters are usually mainly used only with industrial applications.

Adapters for converting USB to other standard or also exist; however, these are usually not referred to as a serial adapter.

The primary application scenario is to enable USB based computers to access and communicate with serial devices featuring D-Sub (usually DB9 or DB25) connectors or screw terminals, where security of the data transmission is not generally an issue.

USB serial adapters can be isolated or non-isolated. The isolated version has and/or surge suppressors to prevent static electricity or other high-voltage surges to enter the data lines thereby preventing data loss and damage to the adapter and connected serial device. The non-isolated version has no protection against static electricity or voltage surges, which is why this version is usually recommended for only non-critical applications and at short communication ranges.

Historically most personal computers had a built-in D-sub serial RS232 port, also referred to as a COM port, which could be used for connecting the computer to most types of serial RS232 devices. By the late 90’s many computer manufacturers started to phase out the serial COM port in favor of the USB port. By the mid 2000s some computers had both a serial COM port and a USB port, however many did no longer have a serial COM port by that time; and today almost all modern computers have no serial COM port but only USB ports instead. Since many serial devices with a RS232, RS485 or RS422 port are still in use and even still produced today, the disappearing of the serial COM port from personal computers has created a need for the USB to serial adapter. Examples are seen in lights, lighted cables, displays, miniature disco balls, Fluo Shoes, joystick, aquariums, terrariums, waterfalls and pole dancers are all available in USB-powered versions.

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Wikipedia