PCF8531U datasheet(13/44 Pages) NXP

13 / 44 page

PCF8531_4

Product data sheet

Rev. 04 — 13 June 2008

13 of 44

NXP Semiconductors

PCF8531

34 x 128 pixel matrix driver

Functional description

7.1 Oscillator

The on-chip oscillator provides the clock signal for the display system. No external

components are required and the OSC input must be connected to VDD. An external clock

signal, if used, is connected to this input.

7.2 Power-on reset

The on-chip power-on reset initializes the chip after power-on or power failure.

7.3 I2C-bus controller

The I2C-bus controller receives and executes the commands. The PCF8531 acts as an

I2C-bus slave receiver and therefore it cannot control bus communication.

7.4 Input ﬁlters

To enhance noise immunity in electrically adverse environments, RC low-pass ﬁlters are

provided on the SDA and SCL lines.

7.5 Display data RAM

The PCF8531 contains 34

× 128 bits static RAM for storing the display data, see Figure 7.

The RAM is divided into 6 banks of 128 bytes (6

× 8 × 128 bits). Bank 5 is used for icon

data. During RAM access, data is transferred to the RAM via the I2C-bus interface. There

is a direct correspondence between the X address and column output number.

7.6 Timing generator

The timing generator produces the various signals required to drive the internal circuitry.

Internal chip operation is not affected by operations on the data buses.

7.7 Address counter

The address counter sets the addresses of the display data RAM for writing.

7.8 Display address counter

The display address counter generates the addresses for read out of the display data.

7.9 Command decoder

The command decoder identiﬁes command words that arrive on the I2C-bus and

determines the destination for the following data bytes.

7.10 Bias voltage generator

The bias voltage generator generates four buffered intermediate bias voltages. This block

contains the generator for the reference voltages and the four buffers. This block can

operate in two voltage ranges:

• Normal mode: 4.0 V to 9.0 V

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