ST62T40B datasheet(51/76 Pages) STMICROELECTRONICS

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ST62T40B/E40B

LCD CONTROLLER-DRIVER (Continued)

4.5.4 Stand by or STOP operation mode

No clock from the main oscillator is available in

STOP mode for the LCD controller, and the con-

troller is switched off when the STOP instruction is

executed. All segment and common lines are then

switched to ground to avoid any DC biasing of the

LCD elements.

Operation in STOP mode remain possible by

switching to the OSC32Khz, by setting the

HF0..HF2 bit of LCDCR accordingly (Table 22).

Care must be taken for the oscillator switching that

LCD function change is only effective at the end of

a frame. Therefore it must be guaranteed that

enough clock pulses are delivered before entering

into STOP mode. Otherwise the LCD function is

switched off at STOP instruction execution.

Table 22. Oscillator Source Selection

4.5.5 LCD Mode Control Register (LCDCR)

Address: DCh - Read/Write

Bits 7-6 = DS0, DS1. Multiplexing ratio select bits.

These bits select the number of common back-

planes used by the LCD control.

Bits 5-3 = HF0, HF1, HF2. Oscillator select bits.

These bits allow the LCD controller to be supplied

with the correct frequency when different high

main oscillator frequencies are selected as system

clock. Table 19 shows the set-up for different clock

crystals.

Bits 2-0 = LF0, LF1, LF2. Base frame frequency

select bits. These bits control the LCD base oper-

ational frequency of the LCD common lines.

LF0, LF1, LF2 define the 32kHz division factor as

shown in Table 23

Table 23. 32kHz Division Factor for Base

Frequency Selection

HF2

HF1

HF0

Division Factor

Clock disabled: Display off

Auxiliary 32kHz oscillator

Reserved

Others

Division from MCU fINT

DS1

DS0

HF2

HF1

HF0

LF2

LF1

LF0

LF2

LF1

LF0

32kHz Division Factor

512

386

256

192

128

Reserved

623

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