[time-nuts] Strange DCF77 master clock data

mike cook mc235960 at gmail.com
Sun Dec 9 12:24:08 UTC 2012


Le 09/12/2012 11:28, Tom Harris a écrit :
> Greetings Time Nuts.
>
> Time related, but unusually so:
>
> I am examining the DCF77 (see http://en.wikipedia.org/wiki/DCF77 for a
> refresher) data output from a master clock intended to drive a series of
> slave clocks operated from 24V DC, interrupted by 100ms or 200ms pulses to
> signal '0'& '1' on the data. What I am seeing is that the "day of week"
> bits 42 through 44 inclusive do not code the day correctly, they seems to
> have a variable offset from the actual day, I have seen an offset from +1
> to +3. The rest of the data, ncluding parity bits, are OK. Today,
> 9/12/2012, the day is Sunday, which should be coded as '7'. However I am
> seeing a value of '3', which is Wednesday.
> Is this normal, do wired DCF77 slave clocks transmit munged dow data to
> prevent them being used with someone else's master clock? If they do I am
> hosed since I am trying to reverse engineer the master clock.
>
   Is it just bit 44 being stuck on zero? or can each dow get varying 
values?

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