Re: Simplest way to propagate a digital pulse?
- From: Max Moor <maxmoor@xxxxxxxxxxxxxxxxxx>
- Date: 4 Apr 2009 06:33:24 GMT
whit3rd <whit3rd@xxxxxxxxx> wrote in news:48b94f59-7441-46bf-926d-
d7ddcac8d4de@xxxxxxxxxxxxxxxxxxxxxxxxxxx:
You presumably also have a 'reset' line somewhere, so that this
bunch of modules will do the same thing all over again someday.
As far as long clock lines are concerned, a differential driver and
receiver can
do it fine (like AM26LS31 and AM26LS32). You can also
daisy-chain (each module receives the clock, buffers it, and
sends it to the next in ripple fashion).
If you really implement the 'wait till module N is done before
module N+1 starts' functionality, every single module is
a point-of-failure for all the rest. That can be made to work,
but this is a kind of control counter, and its state has
100 elements, so the problem is one of one hundred state
bits. If a central controller turns the modules on, the
problem is log_2(100), which is a seven bit state; this
is usually preferable because it is easier to troubleshoot.
I originally thought of using a 10-line ribbon (7 plus a few extra) cable to
run down the line with a decoder at each module for the very reasons you say.
I shied away from that, trading for fewer wires and parts. I'm still not
sure what I should do for sure. I guess that's where prototyping comes in.
.
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