> Is there a way of getting key-pressed data (just 2-bits in my case) to
> the MCU without actively scanning for it ?

Yes.  One way is the port B interrupt on change feature.

> I've been reading all the info I can find, and the only similar examples
> I come across involve keypad scanning.  Maybe I'm a bit naive, but isn't
> it risky to rely on scanning to intercept the data as it is enterred? What
> if your code is busy servicing an interrupt and misses a key-press?

Key presses are very slow events compared to (reasonable) interrupt
handling.  There is no problem if it takes several mS to first notice the
key is down.  You have to debounce it anyway, so no rush.

Especially if you need timing for other tasks, I would check the keypad in a
periodic interrupt, or in the foreground loop with timing from a periodic
interrupt.  I usually use 1mS (1000Hz) interrupt as a master clock, and
don't believe any external mechanical switch has actually changed state
until the new state has been constant for 50mS.  At 20mHz clock, 1mS is 5000
instructions.  Checking the keypad will only use a tiny fraction of that.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olin@embedinc.com, http://www.embedinc.com

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