PCF8574_PCF8574A

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© NXP B.V. 2013. All rights reserved.

Product data sheet

Rev. 5 — 27 May 2013

14 of 33

NXP Semiconductors

PCF8574; PCF8574A

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 Figure 16 to prevent damage to the

device should all ports not be turned on at the same time.

10.4 Migration path

NXP offers newer, more capable drop-in replacements for the PCF8574/74A in newer

space-saving packages.

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.

Fig 16. High current-drive load application

002aah385

P0

P1

P2

P3

P4

P5

P6

P7

SDA

SCL

INT

A0

A1

A2

CORE

PROCESSOR

LOAD

Table 6.

Migration path

Type number

frequency

Voltage range

Number of

addresses

per device

Interrupt

Reset

Total package

sink current

PCF8574/74A

100 kHz

2.5 V to 6 V

8

yes

no

80 mA

PCA8574/74A

400 kHz

2.3 V to 5.5 V

8

yes

no

200 mA

PCA9674/74A

1 MHz Fm+

2.3 V to 5.5 V

64

yes

no

200 mA

PCA9670

1 MHz Fm+

2.3 V to 5.5 V

64

no

yes

200 mA

PCA9672

1 MHz Fm+

2.3 V to 5.5 V

16

yes

yes

200 mA