The CDP1854A and CDP1854AC are 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 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.