> The OP could use the 74HC597 to serially expand the number of inputs.
> Usually it would need three I/O pins, but with a clever trick it is possi=
ble to
> use just two.
> It is possible to expand the input pins to virtually any number, in multi=
ples of
> eight.

With two pins you could bit bang I2C and use an expansion IC like the Phili=
ps PCF8583 or one of the various ones Microchip produce.



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