[time-nuts] GPS DO Alternatives
Bob Camp
lists at rtty.us
Sun Dec 9 22:25:15 UTC 2012
Hi
There are other devices where a simultaneous set and reset will toggle the device.
Since the "useful" operating point is simultaneous inputs, what you are building is a metastability tester.
Bob
On Dec 9, 2012, at 5:00 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
>
> lists at rtty.us said:
>> The flip flop would have a metastable region. It would be quite narrow, but
>> it would be there. As soon as you try to take the square wave into the
>> processor, you are right back to the same problems we've discussed before.
>> The flip flop, run this way does not improve that part of the situation.
>
> That's not the issue I was trying to bring up.
>
> The problem is that set and reset on most FFs are asynchronous. You have to
> look at the fine print in the data sheet to see what happens if they overlap.
> Consider the 74x74 that I looked at. It has true and compliment output
> pins. If set and reset are both active, both outputs go high. So if the
> reset signal comes first, you might expect the FF to get turned off, but with
> that chip, the FF will be high.
>
> (A few FFs have synchronous set and reset, but since there was no mention of
> a clock, I assume we are talking about asynchronous inputs.)
>
>
>
> --
> These are my opinions. I hate spam.
>
>
>
>
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