PCF8545 datasheet(39/68 Pages) NXP

39 / 68 page

NXP Semiconductors

PCF8545

Universal LCD driver for multiplex rates up to 1:8

8.2.8 I2C-bus protocol

The I2C-bus protocol is shown in Figure 30. The sequence is initiated with a START

condition (S) from the I2C-bus controller which is followed by one of the two PCF8545

target addresses available. All PCF8545 with the corresponding A0 level acknowledge in

parallel to the target address. But any PCF8545 with the alternative A0 level ignore the

whole I2C-bus transfer.

After acknowledgement, a control byte follows (see Section 8.1).

The display bytes are stored in the display RAM at the address specified by the RAM

data pointer.

The acknowledgement after each byte is made only by the addressed PCF8545. After

the last data byte, the I2C-bus controller issues a STOP condition (P). Alternatively a

START may be issued to RESTART an I2C-bus access.

EXAMPLES

a) transmit two byte of RAM data

013aaa462

S 0 1 1 1 0

control byte

target address

RAM/command byte

RAM DATA

R/W = 0

S 0 1 1 1 0

b) transmit two command bytes

COMMAND

S 0 1 1 1 0

1 0

COMMAND

c) transmit one command byte and two RAM date bytes

COMMAND

S 0 1 1 1 0

1 0

0 0

RAM DATA

Figure 30. I2C-bus protocol write mode

8.2.8.1 Status read out

Status read out for I2C-bus operation only. This command initiates the read-out of a fixed

value plus the target address bit A0 from the PCF8545. The read-out function allows the

I2C controller to confirm the existence of the device on the I2C-bus.

Bit

Symbol

Value

Description

7 to 1

0101 010

fixed value

read back value is 0101 0100

read back value is 0101 0101

Table 27. Status read out value

If a readout is made, the R/W bit must be logic 1 and then the next data byte following is

provided by the PCF8545 as shown in Figure 31.

PCF8545

All information provided in this document is subject to legal disclaimers.

Product data sheet

Rev. 2 — 4 October 2021

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