pca8574 NXP Semiconductors, pca8574 Datasheet - Page 9

• Manufacturer Part Number: pca8574
• Description: Pca8574/pca8574a Remote 8-bit I/o Expander For I2c-bus With Interrupt
• Manufacturer: NXP Semiconductors

NXP Semiconductors
PCA8574_PCA8574A_2
Product data sheet
8.4 Power-on reset
8.5 Interrupt output (INT)
When power is applied to V
PCA8574/74A in a reset condition until V
condition is released and the PCA8574/74A registers and I
will initialize to their default states. Thereafter V
the device.
The PCA8574/74A provides an open-drain interrupt (INT) which can be fed to a
corresponding input of the microcontroller (see
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 t
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
MICROCOMPUTER
INT
Rev. 02 — 14 May 2007
DD
V
DD
, an internal Power-On Reset (POR) holds the
Remote 8-bit I/O expander for I
PCA8574
device 1
INT
DD
has reached V
DD
Figure
PCA8574
device 2
must be lowered below 0.2 V to reset
INT
8,
Figure
POR
2
C-bus/SMBus state machine
PCA8574/74A
. At that point, the reset
9, and
2
C-bus with interrupt
Figure
© NXP B.V. 2007. All rights reserved.
PCA8574
device 8
002aac682
INT
10). This
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the