Mike Riendeau wrote:
>
>
> If you were using one of the comparators with an interrupt, would
> it be possible to reconfigure the reference voltage "on the fly"
> to provide hysteresis?

Yes, but... Three minor problems. One, the settling time of the 622's
internal voltage reference circuit is relative slow (10 microseconds).
Second, any kind of "software hysteresis" will significantly reduce
the effective comparator speed. For example, the 622 comparators are
spec'd with a 400ns response time, where response time is measured
with "one of the inputs at (Vdd-1.5)/2 and the other transitioning
from Vss to Vdd". Now, even if the reference circuit had an
instantaneous response, the software overhead to change to a new
level would rapidly consume time that could be used for sampling.
(see FYI 4, below). Third, the same comparator is used by both
comparators. If you change the reference voltage for one then you
will affect the performance of the other.

FYI 4, I'm going to use the full bandwidth of these puppies (one
puppy == one comparator). The normal mode is quiescent which
means there is no signal and consequently no change of states
in the comparators outputs. When a signal occurs, it will last
for 100 microseconds or so. I'll catch the initial transition with
an interrupt (after a little of interrupt latency of course). I'll
sample the subsequent transitions once every 400ns.

FYI 5, I've used external comparators and PORT B's change on interrupt
capability with the approach discussed in FYI 4 with great success.

Thanks,
Scott