[time-nuts] GPS DO Alternatives

Bob Camp lists at rtty.us
Sun Dec 9 22:25:15 UTC 2012


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.


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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