1999 Apr 07

8

Philips Semiconductors

Product specification

PCF8575

7

FUNCTIONAL DESCRIPTION

7.1

Quasi-bidirectional I/Os

The PCF8575’s 16 ports (see Fig.7) are entirely independent and can be used either as input or output ports. Input data

is transferred from the ports to the microcontroller in the READ mode (see Fig.10). Output data is transmitted to the ports

in the WRITE mode (see Fig.9).

This quasi-bidirectional I/O can be used as an input or output without the use of a control signal for data direction.

and are switched off by the negative edge of SCL. The I/Os should be HIGH before being used as inputs. After power-on

as all the I/Os are set HIGH all of them can be used as input. Any change in setting of the I/Os as either inputs or outputs

can be done with the write mode. Warning: If a HIGH is applied to an I/O which has been written earlier to LOW, a large

7.2

Addressing

Figures 8, 9 and 10 show the address and timing diagrams. Before any data is transmitted or received the master must

send the address of the receiver via the SDA line. The first byte transmitted after the START condition carries the address

of the slave device and the read/write bit. The address of the slave device must not be changed between the START and

the STOP conditions. The PCF8575 acts as a slave receiver or a slave transmitter.

Fig.7 Simplified schematic diagram of each I/O.

dbook, full pagewidth

MGL540

DQ

CI

CI

S

FF

D

IOH

IOL

IOHt

Q

S

FF

100

µA

to interrupt

logic

VSS

VDD

P00 to P07

P10 to 17

write pulse

data from

shift register

power-on

reset

read pulse

data to

shift register

Fig.8 Byte containing the slave address and the R/W bits.

MGL541

handbook, halfpage

S

0

1

0

0

A2

A1

A0 R/W

A

slave address