2002 Nov 22

9

Philips Semiconductors

Product specification

PCF8574

7

FUNCTIONAL DESCRIPTION

Fig.9 Simplified schematic diagram of each I/O.

handbook, full pagewidth

MBD977

DQ

CI

S

FF

DQ

CI

S

FF

100

µA

to interrupt

logic

VSS

P0 to P7

VDD

write pulse

data from

shift register

power-on

reset

read pulse

data to

shift register

7.1

Addressing

For addressing see Figs 10, 11 and 12.

Fig.10 PCF8574 and PCF8574A slave addresses.

handbook, full pagewidth

MBD973

S

0

1

0

0

A2

A1

A0

0

A

1

0

slave address

slave address

A

S

0

1

1

A2

A1

A0

a. PCF8574.

b. PCF8574A.

Each of the PCF8574’s eight I/Os can be independently used as an input or output. Input data is transferred from the

port to the microcontroller by the READ mode (see Fig.12). Output data is transmitted to the port by the WRITE mode

(see Fig.11).