A USB adapter is a type of protocol converter which is used for converting USB data signals to and from other communications standards. Commonly, USB adapters 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-level UART serial data. The older serial RS423 protocol is rarely used any more, so USB to RS423 adapters are less common. A USB adapter is a type of protocol converter which is used for converting USB data signals to and from other communications standards. Commonly, USB adapters 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-level UART serial data. The older serial RS423 protocol is rarely used any more, so USB to RS423 adapters are less common.