PCF8545ATTSLASHA datasheet(13/72 Pages) NXP

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PCF8545

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Product data sheet

Rev. 1 — 13 November 2013

13 of 72

NXP Semiconductors

PCF8545

Universal LCD driver for multiplex rates up to 1:8

[1]

When RESET is active, the pin OSCCLK is in 3-state.

[2]

In this state, an external clock may be applied, but it is not a requirement.

[3]

9.6 kHz is the nominal frequency with q = 24, see Table 14.

External clock: In applications where an external clock must be applied to the PCF8545,

bit OSC (see Table 10) has to be set logic 1. In this case pin OSCCLK becomes an input.

The OSCCLK signal must switch between the VSS and the VDD voltage supplied to the

chip.

The EFR bit determines the external clock frequency (230 kHz or 9.6 kHz). The clock

frequency (fclk(ext)) in turn determines the LCD frame frequency, see Table 14.

Remark: If an external clock is used, then this clock signal must always be supplied to the

device when the display is on. Removing the clock may freeze the LCD in a DC state

which damages the LCD material.

8.1.4.2

Timing and frame frequency

The timing of the PCF8545 organizes the internal data flow of the device. This includes

the transfer of display data from the display RAM to the display segment outputs. The

timing also generates the LCD frame frequency which it derives as an integer division of

the clock frequency (see Table 14). The frame frequency is a fixed division of the internal

clock or of the frequency applied to pin OSCCLK when an external clock is used.

[1]

Other values of the frame frequency prescaler see Table 18.

When the internal clock is used, or an external clock with EFR = 1, the LCD frame

frequency can be programmed by software in steps of approximately 10 Hz in the range of

60 Hz to 300 Hz (see Table 18). Furthermore the internal oscillator is factory calibrated,

see Table 34 on page 50.

Table 13.

OSCCLK pin state depending on configuration

OSC

COE

EFR

OSCCLK pin[1]

power-down

n.a.

off

n.a.

3-state[2]

power-down

n.a.on

n.a.VDD

power-up

internal oscillator

off

n.a.

3-state

n.a.

9.6 kHz output[3]

external oscillator

n.a.

9.6 kHz

9.6 kHz input

230 kHz

230 kHz input

Table 14.

LCD frame frequencies

Frame frequency

Typical external

frequency (Hz)

Nominal frame

frequency (Hz)

EFR bit

Value of q[1]

9600

200

230000

200

fr LCD



clk ext



-----------------

fr LCD



clk ext



48 q



-----------------

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