Hi The only real limit on a Johnson counter is how clever you get making sure that only one stage is a 1 and all the rest are zeros. There are *lots* of ways to take care of that, each with it's own set of trade offs.
Bob -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Brooke Clarke Sent: Thursday, April 15, 2010 12:00 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] lunatic fringe time standards Hi John: Yes RTL and 3.3 V if I remember correctly. Have Fun, Brooke Clarke http://www.PRC68.com jmfranke wrote: > Wasn't that a RTL 923 and 914? I still have a few from my learning days. > > John WA4WDL > > -------------------------------------------------- > From: "Brooke Clarke" <[email protected]> > Sent: Thursday, April 15, 2010 11:24 AM > To: "Discussion of precise time and frequency measurement" > <[email protected]> > 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. >> http://www.prc68.com/I/comp.shtml#Nixie >> >> Have Fun, >> >> Brooke Clarke >> http://www.PRC68.com >> >> >> 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. >>> >>> Didier >>> >>> ------------------------ Sent from my BlackBerry Wireless thingy >>> while I do other things... >>> >>> -----Original Message----- >>> From: Eugen Leitl<[email protected]> >>> Date: Thu, 15 Apr 2010 13:42:00 >>> To:<[email protected]> >>> Subject: Re: [time-nuts] lunatic fringe time standards >>> >>> On Thu, Apr 15, 2010 at 07:30:27AM -0400, Bob Camp wrote: >>> >>>> Hi >>>> >>>> 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. >>> >>> >> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
