PCA8574_PCA8574A_2

© NXP B.V. 2007. All rights reserved.

Product data sheet

Rev. 02 — 14 May 2007

9 of 27

NXP Semiconductors

PCA8574/74A

8.4 Power-on reset

the device.

8.5 Interrupt output (INT)

The PCA8574/74A provides an open-drain interrupt (INT) which can be fed to a

corresponding input of the microcontroller (see Figure 8, Figure 9, and Figure 10). This

gives these chips a kind of master function which can initiate an action elsewhere in the

system.

signal INT is valid.

The interrupt disappears when data on the port is changed to the original setting or data is

read from or written to the device which has generated the interrupt.

In the write mode, the interrupt may become deactivated (HIGH) on the rising edge of the

write to port pulse. On the falling edge of the write to port pulse the interrupt is definitely

deactivated (HIGH).

The interrupt is reset in the read mode on the rising edge of the read from port pulse.

During the resetting of the interrupt itself, any changes on the I/Os may not generate an

interrupt. After the interrupt is reset any change in I/Os will be detected and transmitted as

an INT.

Fig 10. Application of multiple PCA8574s with interrupt

002aac682

MICROCOMPUTER

INT

PCA8574

INT

PCA8574

INT

device 1

device 2

PCA8574

INT

device 8