The PCA9544A provides 4 interrupt inputs, one for each channel
and one open drain interrupt output. When an interrupt is generated by
any device, it will be detected by the PCA9544A and the interrupt
output will be driven LOW. The channel need not be active for
detection of the interrupt. A bit is also set in the control byte.
Bits 4 – 7 of the control byte correspond to channels 0 – 3 of the
PCA9544A, respectively. Therefore, if an interrupt is generated by
any device connected to channel 2, the state of the interrupt inputs is
loaded into the control register when a read is accomplished.
Likewise, an interrupt on any device connected to channel 0 would
cause bit 4 of the control register to be set on the read. The master
can then address the PCA9544A and read the contents of the
control byte to determine which channel contains the device
generating the interrupt. The master can then reconfigure the
PCA9544A to select this channel, and locate the device generating
the interrupt and clear it. The interrupt clears when the device
originating the interrupt clears.