[time-nuts] Strange DCF77 master clock data

Tom Harris celephicus at gmail.com
Mon Dec 10 11:00:59 UTC 2012

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

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?
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Tom Harris <celephicus at gmail.com>

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