Philips Semiconductors
Product specification
Remote 8-bit I/O expander for I2C-bus
PCF8574
7
FUNCTIONAL DESCRIPTION
V
handbook, full pagewidth
DD
write pulse
100
µA
data from
shift register
D
C
Q
FF
P0 to P7
I
S
power-on
reset
V
SS
D
C
Q
FF
I
read pulse
S
to interrupt
logic
data to
shift register
MBD977
Fig.8 Simplified schematic diagram of each I/O.
7.1
Addressing
For addressing see Figs 9, 10 and 11.
slave address
slave address
handbook, full pagewidth
S
0
1
0
0
A2 A1 A0
0
A
S
0
1
1
1
A2 A1 A0
0
A
MBD973
a.
b.
(a) PCF8574.
(b) PCF8574A.
Fig.9 PCF8574 and PCF8574A slave addresses.
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.11). Output data is transmitted to the port by the
WRITE mode (see Fig.10).
1997 Apr 02
8
NXP [ NXP ]
