PCF8536AT datasheet(11/53 Pages) NXP

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NXP Semiconductors

PCA8551

Automotive 36 × 4 LCD segment driver

7.3 Starting and resetting the PCA8551

If the internal Power-On Reset (POR) is enabled by connecting pin PORE to VDD, the

chip resets automatically when VDD rises above the minimum supply voltage. No further

action is required.

If the internal POR is disabled by connecting pin PORE to VSS, the chip must be reset by

driving the RST pin (PCA8551A only) to logic 0 for at least 10 μs, see Figure 6.

tw(rst) = 10 µs

minimum

tw(rst) = 10 µs

minimum

VDD(min)

VDD

RST

Valid reset pulse

during power-up

Valid reset pulse

after power-up

aaa-017468

Figure 6. Reset pulse timing

Alternatively a software reset can be applied (see Section 7.3.4).

Following a reset, the register 00h has to be rewritten with 0h by the next command byte

or the address pointer AP[4:0] has to be set to the required address after a new START

procedure. See also application information in Section 15.

7.3.1 Power-down mode

After a reset, the PCA8551 remains in power-down mode. In power-down mode the

oscillator is switched off and there is no output on pin CLK. The register settings remain

unchanged and the bus remains active. To enable the PCA8551, bit DE (command

Display_ctrl_1, see Table 6) must be set to logic 1.

7.3.2 Power-On Reset (POR)

If pin PORE is connected to VDD, the PCA8551 comprises an internal POR, which puts

the device into the following starting conditions:

• 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

• The bus interface is initialized

Remark: The internal POR can be disabled by connecting pin PORE to VSS. In this

case, the internal registers are not defined and require a hardware reset according to

Section 7.3.3 or a software reset, see Section 7.3.4.

PCA8551

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Product data sheet

Rev. 3.1 — 3 May 2021

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