PCF8537 datasheet(14/82 Pages) NXP

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PCF8537

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Product data sheet

Rev. 1 — 31 May 2012

14 of 82

NXP Semiconductors

PCF8537

Industrial LCD driver for multiplex rates up to 1:8

8.1.12.1

Timing and frame frequency

The timing of the PCF8537 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. The frame frequency is a fixed division of

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

When the internal clock is used, the clock frequency can be programmed by software

such that the nominal frame frequency can be chosen in steps of 10 Hz in the range of

60 Hz to 300 Hz (see Table 17). Furthermore the nominal frame frequency is

factory-calibrated with an accuracy of ±15 %.

When the internal clock is enabled at pin CLK by using bit COE, the duty ratio of the clock

may change when choosing different values for the frame frequency prescaler. Table 17

shows the different output duty ratios for each frame frequency prescaler setting.

8.1.13 Command: Bank-select

For the multiplex drive modes 1:4, 1:2, and the static drive mode, it is possible to write

data to one area of the RAM while displaying from another. These areas are named RAM

banks. There are two banks, 0 and 1. Figure 39 on page 50 and Figure 40 on page 50

show the concept. The Bank-select command controls where data is written to and where

it is displayed from.

[1]

Default value.

8.1.14 Command: Write-RAM-data

By setting the RS bit of the control byte to logic 1, all data transferred is interpreted as

RAM data and placed in the RAM in accordance with the current setting of the RAM

address pointer (see Section 8.1.11 on page 12). Definition of the RS can be found in

Table 30 on page 52.

Remark: After Power-On Reset (POR) the RAM content is random and should be brought

to a defined status by clearing it (setting it to logic 0).

Table 18.

Bank-select - bank select command bit description

For further information, see Section 8.9 on page 50.

Bit

Symbol

Binary value

Description

7 to 2

000010

fixed value

1IBS

selects RAM bank to write to

0[1]

Bank 0

Bank 1

0OBS

selects RAM bank to read from to the LCD

0[1]

Bank 0

Bank 1

Table 19.

Write-RAM-data - write RAM data command bit description

For further information, see Section 8.8 on page 44.

Bit

Symbol

Binary value

Description

7 to 0

B[7:0]

00000000 to

11111111

writing data byte-wise to the RAM

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