This post continues after Interrupts Squared.

This is just a quick update to show off the changes done to add a secondary mcp23017. The hardware change is pretty simple, just add it to the existing lines.

Pictures

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Most important is probably that the A0 address pin is set to high instead of low. Schematic:

And new pictures (notice some re-wiring):

Code Changes

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On the code side this commit contains the interesting changes. The following are mostly cleanup and re-enabling interrupt style setup.

The uint16_t state became a uint32_t state to fit all bits. Doesn’t really change anything about execution, since it still fits into a register.

And as fair warning, you need to update code with the new hardware and setup both mcp23017, otherwise the interrupt pin might not behave properly.