MCP23008 IO Expander - Interrupt control

 Now I found that the INTCAP register seems to have a very strong memory, and I still have not found a way to reset its contents (perhaps except by resetting MCP23008).  So I gave up using it and instead used the hardware INT pin to detect interrupt.

I searched my old posts and found that INT is connected as follows

1. INT pulled up by 100K regsister to 3V3.

2. INT connected the through another 100K to base of bipolar junction transistor CS9012, which drives a red LED and 560R series resistor.  The power supply is 3V3.

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