[time-nuts] lunatic fringe time standards
jmfranke at cox.net
Thu Apr 15 15:40:14 UTC 2010
Wasn't that a RTL 923 and 914? I still have a few from my learning days.
From: "Brooke Clarke" <brooke at pacific.net>
Sent: Thursday, April 15, 2010 11:24 AM
To: "Discussion of precise time and frequency measurement"
<time-nuts at febo.com>
Subject: Re: [time-nuts] lunatic fringe time standards
> Hi Didier:
> When working with high speed data, for example an IDE hard drive, where
> there are parallel data lines you get into the same problem as you have
> with a shaft encoder where there are parallel binary data lines. In the
> case of the shaft encoder mechanical misalignment can cause huge errors at
> the transitions and in the hard drive jitter and time delays can cause
> similar problems. I think that was one of the main motivations to go to a
> serial hard drive interface (SATA).
> When in college I used a Johnson counter made from the first ICs from
> Fairchild, i.e. the 723 flip-flop and the 714 two input gate. The beauty
> of the Johnson counter is that you can decode it's state with ten each two
> input gates.
> Have Fun,
> Brooke Clarke
> Didier Juges wrote:
>> I believe Gray code was invented to support absolute mechanical position
>> encoders, where the speed of the electronics is high compared to the
>> speed of the hardware being monitored. It eliminates the potentially
>> large error between two positions since only one bit changes at a time.
>> This is done at the expense of complicated logic, which goes against
>> I don't think Gray code has ever been used to implement fast electronic
>> counters. That's what synchronous counters are for, and when synchronous
>> counters are not fast enough, use a prescaler. It will just take more
>> time to get the precision you need.
>> Unless you need fractional Hz resolution at THz speed, a prescaler is the
>> way to go.
>> ------------------------ Sent from my BlackBerry Wireless thingy while I
>> do other things...
>> -----Original Message-----
>> From: Eugen Leitl<eugen at leitl.org>
>> Date: Thu, 15 Apr 2010 13:42:00
>> To:<time-nuts at febo.com>
>> Subject: Re: [time-nuts] lunatic fringe time standards
>> On Thu, Apr 15, 2010 at 07:30:27AM -0400, Bob Camp wrote:
>>> I'm not 100% sure I understand exactly what you are thinking about
>>> setting up.
>> This is completely theoretical at this point. Just the required geometry
>> size would be prohibitive.
>>> My guess is that the counter needs to run at the same THz speed as
>>> the oscillator. That's pretty fast. I suspect that what ever you use,
>>> speed / propagation delay in the counter it's self will be an issue.
>>> That will get you back to either a ripple counter or a Johnson counter.
>> Wouldn't you get large errors when you caught a ripple
>> during readout? That wouldn't be a problem with a Gray code.
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