The MA28151 is used as a peripheral device and is programmed by the CPU to operate using virtually any serial data transmission technique presently in use (including IBM "bi-sync"). The USART accepts data characters from the CPU in parallel format and then converts them into a continuous serial data stream for transmission. Simultaneously, it can receive serial data streams and convert them into parallel data characters for the CPU. The USART signals the CPU whenever it receives a character for transmission or whenever it receives a character for the CPU. The CPU can read the complete status of the USART at any time, including data transmission errors and control signals such as SYNDET and TxEMPTY.