AN2687 Datasheet, PDF (1/22 Pages) STMicroelectronics – STM8S20xxx LCD software driver

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.
April 2009
Doc ID 14296 Rev 1
1/22