AN1048 Datasheet, PDF (1/21 Pages) STMicroelectronics – ST7 software LCD driver

AN1048
Application note
ST7 software LCD driver
Introduction
This note describes a technique for driving Liquid Crystal Displays (LCD) with any standard
ST7 Microcontroller (MCU) i.e without any specific on-chip LCD driver hardware. This
technique offers a solution for applications which require a display at low cost together with
the versatile capabilities of the standard ST7 MCUs. This note also provides a technique to
control the LCD contrast through software.
After an introduction on LCDs in Section 1, Section 2 & 3 of this note describes the typical
waveforms required to drive an LCD with a multiplexing rate of 1 or 2 (duplex) and 4
(quadruplex). Section 3 presents a solution based on a standard ST7 MCU directly driving a
quadruplex LCD. This solution can be implemented with any ST7 MCU as it only requires
the standard I/O ports and one timer, both of which are standard features on all ST7 MCUs.
Section 4 describes how to control the contrast through software. Finally, Section 5 gives a
brief overview of the LCD demo board including the board schematics. The demo board,
based on a ST72F321B microcontroller, allows the user to develop and test applications
using an LCD device.
The program size (~300 bytes), the CPU load required for controlling the LCD (0.2%), and
the number of external components is kept to the minimum (two external resistors per COM
line). The number of I/O’s is the same as a solution using an on-chip LCD hardware driver or
an external hardware LCD driver. With software contrast control, it is a very flexible solution
that can be adapted easily to a range of applications.
May 2006
Rev 5
1/21
www.st.com