April 2009

Doc ID 14296 Rev 1

1/22

AN2687

Application note

STM8S20xxx

LCD software driver

Introduction

This application note describes two different methods for driving liquid crystal displays

(LCD) with any standard STM8S20xxx microcontroller (MCU), without any specific on-chip

LCD driver hardware:

●

the first method uses the timer 2 channel resource and also allows LCD contrast

control through software

●

the second method uses the Auto-wakeup mode only

This application note starts with an introduction on LCDs in Section 1: LCD principle and

Section 2: LCD drive signals.

Section 3 then presents a solution based on a standard STM8S20xxx MCU directly driving a

quadruplex LCD. This solution can be implemented with any MCU as it only requires the

standard I/O ports and some timings.

Section 4 gives consumption considerations. Section 5 describes how to control contrast

through software: for this purpose, two push-buttons connected to two standard I/Os are

used. Finally, Section 6 gives an overview of the LCD demo board based on an

STM8S20xxx microcontroller, and provides the board schematics.

For more information on the LCD drive theory, please refer also to AN1048.

The number of external components is kept to a minimum of two external resistors per COM

line. The number of I/Os depends on the number of LCD segments used. Software contrast

control is a very flexible solution that can be easily adapted to a wide range of applications.