The CDP1854A/3 and CDP1854AC/3 are high reliability silicon gate CMOS Universal Asynchronous Receiver/Transmitter (UART) circuits. They are designed to provide the necessary formatting and control for interfacing between serial and parallel data. For example, these UARTs can be used to interface between a peripheral or terminal with serial I/O ports and the 8-bit CDP1800-series microprocessor parallel data bus system. The CDP1854A/3 is capable of full duplex operation, i.e., simultaneous conversion of serial input data to parallel output data and parallel input data to serial output data.