ST72589BW datasheet(42/158 Pages) STMICROELECTRONICS

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ST72589BW, ST72389BW

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7 ON-CHIP PERIPHERALS

7.1 LCD DRIVER

7.1.1 Introduction

The LCD driver controls up to 60 segments and 8

backplanes to drive up to 60x8 (480) or 60x4(240)

LCD segments.

Two programmable display modes (1/4 and 1/8

duty cycle) with 4 LCD drive frequencies can be

selected by software.

The parameters to display are stored in a 60-byte

LCD dual port RAM.

Four different main oscillator clocks can be select-

ed as clock for the peripheral.

– 8, 4, 2, 1 MHz fCPU software selectable.

The peripheral can be switched off by software to

reduce the power consumption while it is not used.

Figure 25. LCD Frequency Generator Block Diagram

7.1.2 Voltage references

The display voltage levels are supplied by an ex-

ternal resistor chain as shown in Figure 26 This

LCD driver needs 5 external voltage references

through 5 pins (GLCD, 1/4VLCD, 1/2VLCD,

3/4VLCD, VLCD).

The resistors used must have good tolerance

matching within 1% to avoid DC voltage levels on

the liquid crystal device. DC levels trigger elec-

trode reactions in the liquid crystal cell, causing a

rapid deterioration of the display quality.

Note: To avoid damaging the device, VLCD supply

voltages must always be supplied with more than

VDD or they have to be left unconnected.

Figure 26. LCD External Supply Network

CLOCK

DIVIDER

fFR

fLCDin ≈ 16KHz

fCPU

fLCD ≈ 0.5...2KHz

DIV 8,16,24,32

DCS

CD1

CD0 LCDE

FS1

FS0

BACKPLANE

MUX

MAIN

OSCILLATOR

(SEG, COM)

RLCD1

VLCD

EXTERNAL VLCD

3/4VLCD

1/2VLCD

1/4VLCD

GLCD

RLCD2

RLCD3

RLCD4

CLCD1

CLCD2

CLCD3

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