The PCA9544A provides four interrupt inputs (one for each channel) and one open-drain interrupt output. When an interrupt is generated by any device, it is detected by the PCA9544A, and the interrupt output is driven low. The channel does not need to be active for detection of the interrupt. A bit also is set in the control register (see Table 8-2).

Bits 4–7 of the control register correspond to channels 0–3 of the PCA9544A, respectively. Therefore, if an interrupt is generated by any device connected to channel 1, 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 causes bit 4 of the control register to be set on the read. The master then can address the PCA9544A and read the contents of the control register to determine which channel contains the device generating the interrupt. The master can reconfigure the PCA9544A to select this channel and locate the device generating the interrupt and clear it. Once the device responsible for the interrupt clears, the interrupt clears.

It should be noted that more than one device can provide an interrupt on a channel, so it is up to the master to ensure that all devices on a channel are interrogated for an interrupt.

The interrupt inputs can be used as general-purpose inputs if the interrupt function is not required.

If unused, interrupt input(s) must be connected to V_CC.