1999 Aug 05

6

Philips Semiconductors

Product specification

PCF8575C

6

FUNCTIONAL DESCRIPTION

6.1

Quasi-bidirectional I/Os

The 16 ports (see Fig.3) 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.6). Output data is transmitted to the ports in the WRITE

mode (see Fig.5).

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

loaded output. This strong pull-up turns on when the output is written HIGH, and is switched off by the negative edge of

SCL. After this short period the output is in 3-state mode. The I/O should be written HIGH before being used as an input.

After power-on as all the I/Os are set to 3-state all of them can be used as inputs. 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

6.2

Addressing

Figures 4, 5 and 6 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 PCF8575C acts as a slave receiver or a slave transmitter.

handbook, full pagewidth

MGS632

DQ

CI

CI

S

FF

D

IOL

IOHt

Q

S

FF

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.3 Simplified schematic diagram of each I/O.

MGL541

handbook, halfpage

S

0

1

0

0

A2

A1

A0 R/W

A

slave address

Fig.4 Byte containing the slave address and the R/W bits.