PCA9674ATS datasheet(15/34 Pages) PHILIPS

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PCA9674_PCA9674A_2

Product data sheet

Rev. 02 — 12 October 2006

15 of 34

NXP Semiconductors

PCA9674/74A

Remote 8-bit I/O expander for Fm+ I2C-bus with interrupt

8.4 Power-on reset

When power is applied to VDD, an internal Power-On Reset (POR) holds the

PCA9674/74A in a reset condition until VDD has reached VPOR. At that point, the reset

condition is released and the PCA9674/74A registers and I2C-bus/SMBus state machine

will initialize to their default states. Thereafter VDD must be lowered below 0.2 V to reset

the device.

8.5 Interrupt output (INT)

The PCA9674/74A provides an open-drain interrupt (INT) which can be fed to a

corresponding input of the microcontroller (see Figure 14, Figure 15, and Figure 16). This

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

system.

An interrupt is generated by any rising or falling edge of the port inputs. After time tv(D) the

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 16. Application of multiple PCA9674s with interrupt

002aac122

VDD

MICROCOMPUTER

INT

PCA9674

INT

PCA9674

INT

device 1

device 2

PCA9674

INT

device 8

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