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Post: Hi eirik I have uploaded a new interrupt demo to GitHub at [url=https://github.com/abelectronicsuk/ABElectronics_CPP_Libraries/blob/master/ExpanderPi/demos/demo-io-interrupts.cpp]demo-io-interrupts.cpp[/url] which shows the basics of how interrupts work on the Expander Pi. The interrupt hardware built into the MCP23017 controller allows you to trigger an output on the IA and IB pins when an event occurs on the input pins. You still need to regularly check the status of the interrupts to see if an event has occurred but it does allow you to check at less frequent intervals without missing out on a change on one of the input pins. We have two interrupt tutorials for the IO Pi which use the same IO chip as the Expander Pi. [url=/kb/article/1087/io-pi-plus-tutorial-3-introducing-interrupts]Introducing Interrupts[/url] [url=/kb/article/1088/io-pi-plus-tutorial-4-more-interrupts]More Interrupts[/url] Both tutorials use Python instead of C++ but I have written our libraries to be similar across the different programming languages so you should be able to use the tutorials to get a good idea of how interrupts work in C++. For a more detailed explanation of how the interrupts work in the MCP23017, I would recommend reading the [url=/docs/pdf/microchip-mcp23017.pdf]datasheet for the MCP23017[/url]. Page 27 has a description of the interrupt logic.