Datasheet

PCA9674_PCA9674A All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 7 — 30 May 2013 17 of 40
NXP Semiconductors
PCA9674; PCA9674A
Remote 8-bit I/O expander for Fm+ I
2
C-bus with interrupt
8.4 Power-on reset
When power is applied to V
DD
, an internal Power-On Reset (POR) holds the PCA9674;
PCA9674A in a reset condition until V
DD
has reached V
POR
. At that point, the reset
condition is released and the PCA9674; PCA9674A registers and I
2
C-bus/SMBus state
machine will initialize to their default states of all I/O inputs with weak current source to
V
DD
. Thereafter V
DD
must be lowered below V
POR
and back up to the operation voltage for
power-on reset cycle.
8.5 Interrupt output (INT)
The PCA9674/74A provides an open-drain output (INT) which can be fed to a
corresponding input of the microcontroller (see Figure 15
). As soon as a port input is
changed, the INT
will be active (LOW) and notify the microcontroller.
An interrupt is generated at any rising or falling edge of the port inputs. After time t
v(Q)
, the
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 become de-activated (HIGH) on the rising edge of
the acknowledge bit of the data 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 13
).
The interrupt is reset (HIGH) in the Read mode on the rising edge of the acknowledge of
slave address byte and on the rising edge of the read from port pulse (see Figure 14
).
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 15. Application of multiple PCA9674s with interrupt
002aac122
V
DD
MICROCOMPUTER
INT
PCA9674
INT
PCA9674
INT
device 1 device 2
PCA9674
INT
device 8