NXP Semiconductors
PCF8574; PCF8574A
Remote 8-bit I/O expander for I
2
C-bus with interrupt
while (INT == 1); //Monitor the interrupt pin. If INT = 1 do nothing
//When INT = 0 then read input ports
<S> <slave address read> <ACK> <1010 0010> <NACK> <P> //Read PCF8574 data
If (P0 == 0) //Temperature sensor activated
{
// write to PCF8574 with data 0010 1011b to turn on LED (P7), on Switch (P3)
and keep P[1:0] as input ports.
<S> <0100 0000> <ACK> <0010 1011> <ACK> <P> // Write to PCF8574
}
10.3 High current-drive load applications
The GPIO has a minimum guaranteed sinking current of 10 mA per bit at 5 V. In
applications requiring additional drive, two port pins may be connected together to sink up
to 20 mA current. Both bits must then always be turned on or off together. Up to five pins
can be connected together to drive 80 mA, which is the device recommended total limit.
Each pin needs its own limiting resistor as shown in
to prevent damage to the
device should all ports not be turned on at the same time.
V
DD
V
DD
V
DD
CORE
PROCESSOR
SDA
SCL
INT
A0
A1
A2
P0
P1
P2
P3
P4
P5
P6
P7
LOAD
002aah385
Fig 16. High current-drive load application
10.4 Migration path
NXP offers newer, more capable drop-in replacements for the PCF8574/74A in newer
space-saving packages.
Table 6.
Migration path
I
2
C-bus
frequency
100 kHz
400 kHz
1 MHz Fm+
1 MHz Fm+
1 MHz Fm+
Voltage range
Number of
addresses
per device
8
8
64
64
16
Interrupt
Reset
Total package
sink current
80 mA
200 mA
200 mA
200 mA
200 mA
Type number
PCF8574/74A
PCA8574/74A
PCA9674/74A
PCA9670
PCA9672
2.5 V to 6 V
2.3 V to 5.5 V
2.3 V to 5.5 V
2.3 V to 5.5 V
2.3 V to 5.5 V
yes
yes
yes
no
yes
no
no
no
yes
yes
PCA9670 replaces the interrupt output of the PCA9674 with hardware reset input to retain
the maximum number of addresses and the PCA9672 replaces address A2 of the
PCA9674 with hardware reset input to retain the interrupt but limit the number of
addresses.
PCF8574_PCF8574A
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2013. All rights reserved.
Product data sheet
Rev. 5 — 27 May 2013
14 of 33
PHILIPS [ NXP SEMICONDUCTORS ]
