March 2013

DocID9986 Rev 2

1/22

AN1753

Application note

Software UART using ST7LITE0 12-bit autoreload timer

Introduction

This application note describes a software implementation of a Universal Asynchronous

Receiver/Transmitter (UART). This can be used on devices with no on-chip SCI peripheral.

In this example, a software UART is implemented for the ST7LITE0, using the 12-bit

Autoreload timer and two I/O ports for asynchronous receive and transmit. The UART

software provides the following features:

• Half-duplex operation

• Asynchronous operation

• Flexible data formats (7 or 8 data bits, 1 or 2 stop bits)

• Baud rate: 2400 to 19200 baud

To test this interrupt-driven software UART, you can use the “Hyperterminal” application

running on a Windows PC.

The program code is quite small (357 bytes) and can easily be adapted to specific

application requirements.

Table 1 lists the microcontrollers and software concerned by this application note.

Table 1. Applicable products and software

Type

Part numbers or product categories

Microcontrollers

ST7LITE02Y0, ST7LITE05Y0, ST7LITE09Y0

Software

STSW-ST7094

www.st.com