AN1447/0901

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AN1447

APPLICATION NOTE

SOFTWARE DRIVER FOR

4-MULTIPLEXED LCD WITH A STANDARD ST62

by Microcontroller Division Applications

DESCRIPTION

This note describes a technique for driving a 4-multiplexed Liquid Crystal Display (LCD) with

a standard ST62 microcontroller (MCU), without any dedicated LCD driver peripheral. This

technique offers a display capability for applications which require a small display at a low cost

together with the versatile capabilities of the standard ST62xx MCU.

Higher display requirements are easily handled by dedicated members of the ST62 MCU

family, for example the ST6240. Solutions on how to use a standard ST6 to drive an LCD with

a multiplexing ratio of 2 (duplex) can be found in Application Note AN594.

The first section of this note describes the typical waveforms required to drive an LCD, first

without multiplexing (“direct” drive), then with a multiplexing rate of 4. The second section ex-

plains how to use a software library written in assembly language (MAST6 syntax) imple-

menting a solution based on a standard ST62 MCU driving directly the LCD.

The program size and the CPU time occupation due to the LCD drive are minimized. Conse-

quently many additional tasks can be added to the MCU program. Only few cheap additional

components are required.

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