A UART, universal asynchronous receiver / transmitter is responsible for performing the main task in serial communications with computers. The device changes incomming parallel information to serial data which can be sent on a communication line. A second UART can be used to receive the information. The UART performs all the tasks, timing, parity checking, etc. needed for the communication. The only extra devices attached are line driver chips capable of transforming the TTL level signals to line voltages and vice versa.
To use the UART in different environments, registers are accessible to set or review the communication parameters. Setable parameters are for example the communication speed, the type of parity check, and the way incomming information is signalled to the running software.