PCA8575_2 © NXP B.V. 2007. All rights reserved.
Product data sheet Rev. 02 — 21 March 2007 11 of 30
NXP Semiconductors
PCA8575
Remote 16-bit I/O expander for 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 PCA8575 in
a reset condition until V
DD
has reached V
POR
. At that point, the reset condition is released
and the PCA8575 registers and I
2
C-bus/SMBus state machine will initialize to their default
states. Thereafter V
DD
must be lowered below 0.2 V to reset the device.
8.5 Interrupt output (INT)
The PCA8575 provides an open-drain interrupt (INT) which can be fed to a corresponding
input of the microcontroller (see Figure 12, Figure 13, and Figure 14). 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 t
v(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 14. Application of multiple PCA8575s with interrupt
002aac676
V
DD
MICROCOMPUTER
INT
PCA8575
INT
PCA8575
INT
device 1 device 2
PCA8575
INT
device 8
