PCF8536AT datasheet(12/53 Pages) NXP

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NXP Semiconductors

PCA8551

Automotive 36 × 4 LCD segment driver

Remark: For power-on with a slowly starting power supply, see Section 15.1.

7.3.3 Hardware reset: RST pin (only PCA8551A)

At power-on the PCA8551A can be reset to the following starting conditions by pulling pin

RST low:

• All backplane and segment outputs are set to VSS

• The selected drive mode is: 1:4 multiplex with 1⁄3 bias

• Blinking is switched off

• The address pointer is cleared (set to logic 0)

• The display and the internal oscillator are disabled

• The display registers are set to logic 0

Remark: The hardware reset overrides the POR see Section 7.3.2.

7.3.4 Command: Software_reset

The internal registers including the display registers and the address pointer (set to logic

0) of the device are reset by the Software_reset command.

Bit

Symbol

Value

Description

software reset

0000 0000[2]

no reset

7 to 0

SR[7:0][1]

0010 1100

software reset

Table 8. Software_reset - software reset command register (address 00h) bit

description

[1]

Software_reset only generates a reset pulse, therefore this register always reads back as 00h.

[2]

Default value.

7.4 Display data register mapping

The example in Table 9 and Figure 7 illustrates the segment and backplane mapping of

the display in relation to the display RAM.

For example, in 1:4 multiplex drive mode, the backplanes are served by signals COM0 to

COM3 and the segments are driven by signals SEG0 to SEG35. Contents of addresses

04h to 08h are allocated to the first row (COM0) starting with the LSB driving the leftmost

element and moving forward to the right with increasing bit position. If a bit is logic 0, the

element is off, if it is logic 1 the element is turned on. All register content is LSB to MSB

left to right. Addresses 09h to 0Dh serve COM1 signals, addresses 0Eh to 12h serve

COM2 signals, and addresses 13h to 17h serve COM3 signals.

For displays with fewer segments/elements the unused bits are ignored.

Segments

SEG0 to SEG7

SEG8 to SEG15

SEG16 to SEG23

SEG24 to SEG31

SEG32 to SEG35

Backplanes[1]

LSB

MSB

LSB

MSB

LSB

MSB

LSB

MSB

LSB

MSB

1:4 multiplex drive mode

COM0

content of 04h

content of 05h

content of 06h

content of 07h

content of 08h

Table 9. Register to segment and backplane mapping

PCA8551

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Product data sheet

Rev. 3.1 — 3 May 2021

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