[sdiy] Binary state change detector

[Peter Grenader]

Does anyone have a clue why this letter popped up again??? I didn't resend
it.

'tis wierd.




Peter Grenader wrote:

> I am looking for a circuit that detects when the state (number) of a  four
> bit binary word changes state.
> 
> I've been putzing around with the idea of using a 74C85 in conjunction with
> a 4242 (using the 42 to latch the the last occurrence of change and feed it
> back into the C85 for the next comparison, and then running that output
> through a oneshot to keep it from disappearing as soon as it is sensed, but
> to this I have a question:
> 
> How short of a incoming pulse does a oneshot require in order to react?  For
> instance, another perfect example is a sequencer reset pulse coming from one
> of it's stage gate outputs.  As soon as it goes high, the reset function
> occurs and the gate is no longer high.  Will that pulse width, as short as
> it is, be long enough for a oneshot to react?  Although this isn't my
> application, its the same idea and if it's long enough, me thinks I've got
> the circuit I need here.
> 
> If not, I'm totally screwed and am asking the masters here if they have any
> other suggestions.
> 
> thanks in advance,
> 
> Peter
>