PCF8574_PCF8574A

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Product data sheet

Rev. 5 — 27 May 2013

10 of 33

NXP Semiconductors

PCF8574; PCF8574A

8.5 Interrupt output (INT)

The PCF8574/74A provides an open-drain output (INT) which can be fed to a

corresponding input of the microcontroller (see Figure 10). As soon as a port input is

changed, the INT will be active (LOW) and notify the microcontroller.

signal INT is valid.

The interrupt will reset to HIGH when data on the port is changed to the original setting or

data is read or written by the master.

In the Write mode, the interrupt may be reset (HIGH) on the rising edge of the

acknowledge bit of the address byte and also on the rising edge of the write to port pulse.

The interrupt will always be reset (HIGH) on the falling edge of the write to port pulse (see

Figure 8).

The interrupt is reset (HIGH) in the Read mode on the rising edge of the read from port

pulse (see Figure 9).

During the interrupt reset, any I/O change close to the read or write pulse may not

generate an interrupt, or the interrupt will have a very short pulse. After the interrupt is

reset, any change in I/Os will be detected and transmitted as an INT.

At power-on reset all ports are in Input mode and the initial state of the ports is HIGH,

therefore, for any port pin that is pulled LOW or driven LOW by external source, the

interrupt output will be active (output LOW).

Fig 10. Application of multiple PCF8574/74As with interrupt

002aad634

MICROCONTROLLER

INT

PCF8574

INT

PCF8574

INT

device 1

device 2

PCF8574A

INT

device 16