PCF8545 datasheet(12/72 Pages) NXP

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PCF8545

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Product data sheet

Rev. 1 — 13 November 2013

12 of 72

NXP Semiconductors

PCF8545

Universal LCD driver for multiplex rates up to 1:8

8.1.4.1

Oscillator

The system is designed to operate from a 9.6 kHz or a 230 kHz clock. This clock can be

sourced internally or externally. The internal logic and LCD drive signals of the PCF8545

are timed either by the internal oscillator or from the clock externally supplied.

Internal clock: When the internal oscillator is used, all LCD signals are generated from it.

The oscillator runs at nominal 230 kHz. The relationship between this frequency and the

LCD frame frequency is detailed in Section 8.1.7. Control over the internal oscillator is

made with the OSC bit (see Section 8.1.4).

It is possible to make the internal oscillator signal available on pin OSCCLK by using the

oscillator-control command (see Table 10) and configuring the clock output enable (COE)

bit. If not required, the pin OSCCLK should be left open or connected to VSS. At power-on

the signal at pin OSCCLK is disabled and pin OSCCLK is in 3-state.

Clock output is only valid when using the internal oscillator. The signal appears on the

OSCCLK pin.

An intermediate clock frequency is available at the OSCCLK pin. The duty cycle of this

clock varies with the chosen divide ratio.

(1) Can only be used with the internal oscillator (OSC = 0).

(2) Can only be used with an external oscillator (OSC = 1).

(3) Nominal value for divide factor q is 24; source clock is 230 kHz (see Section 8.1.7).

Fig 7.

Oscillator selection

Table 11.

Valid combinations of bits OSC, EFR, and COE

OSC

COE

EFR

OSCCLK pin

Clock source

not used

inactive;

may be left floating

internal oscillator used

not used

output of internal oscillator

frequency (prescaler)

internal oscillator used

not used

9.6 kHz input

OSCCLK pin

not used

230 kHz input

OSCCLK pin

Table 12.

Typical use of bits OSC, EFR, and COE

Usage

OSC

COE

EFR

LCD with internal oscillator

not used

LCD with external oscillator (230 kHz)

not used

LCD with external oscillator (9.6 kHz)

not used

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