This application note describes a software implementation of a Universal Asynchronous Receiver/Transmitter (UART) that can be used on devices, like the ST7LITE0, with no on-chip SCI peripheral. In this example, a software UART is implemented for the ST7FLITE0, using the 12-bit Autoreload timer and two I/O ports for asynchronous receive and transmit. The UART software provides features such as half-duplex operation, asynchronous operation, flexible data formats (7 or 8 data bits, 1 or 2 stop bits), and baud rates ranging from 2400 to 19200 baud. The interrupt-driven software UART can be tested using the Hyperterminal application on a Windows PC. The program code is small (357 bytes) and can be easily adapted to specific application requirements.