Detect change of state - boolean logic

mojorizing

Help me out here.....

to detect a change of state (xstate) on a prop pin it would be the following code for low to high...

xstate := newstate ^ oldstate & newstate   ' detect change of bits, 0->1

what is the logic to detect a change from high to low?

oldstate, newstate, and xstate refer to the states of 4 adjacent pins wired to 4 push buttons held high, going low when pressed.

I could use a bitwise not to invert inputs, but is there other way? I'm cross-eyed from working out truth tables.

Phil Pilgrim (PhiPi)

Try these:

xstate := !oldstate & newstate 'Detect 0->1.
xstate := oldstate & !newstate 'Detect 1->0.

-Phil

mojorizing

That does it!

Thanks, Phil