[time-nuts] lunatic fringe time standards
brooke at pacific.net
Thu Apr 15 16:00:04 UTC 2010
Yes RTL and 3.3 V if I remember correctly.
> Wasn't that a RTL 923 and 914? I still have a few from my learning days.
> John WA4WDL
> 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 speed.
>>> 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
>>> 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
>>> 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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