[time-nuts] Strange DCF77 master clock data

Chris Howard chris at elfpen.com
Mon Dec 10 12:44:08 UTC 2012

If it were me, I'd suspect that my window of bits is off
to the left or right by one bit.  The old "first bit is
called zero" problem.

And the relationship between 7-> 3  and 5-> 1 makes me


On 12/10/2012 5:00 AM, Tom Harris wrote:
> I am logging the data from this strange master clock, and the none of the
> bits 42 through 44 are stuck. Good idea, though. I have just checked
> tonight, and the DOW is indicating as 5 (Friday), despite it only being
> Monday.
> Good idea though.
> On 9 December 2012 23:24, mike cook <mc235960 at gmail.com> wrote:
>> 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<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?
>> --
>> Les chiens aboient, et la caravane passe.
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