[time-nuts] Strange DCF77 master clock data

mike cook mc235960 at gmail.com
Mon Dec 10 15:52:43 UTC 2012

```Le 10/12/2012 13:44, Chris Howard a écrit :
> 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
> wonder.
>
> Chris
>
>
>
> 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.
I guess you will need to log a weeks worth to see if there is a logical
pattern.
How about flipped bit 44 ? That would give the seen Sunday and Monday
values. Tomorrow would be 6.
Mon = 101  5
Tue = 110   6
Wed = 111 7
Thu = 000 0
Fri = 001  1
Sat = 010 2
Sun = 011 3

The parity being good may mean that it is not an error, but a feature.
>>
>> 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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>>
>>
>
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--
Les chiens aboient, et la caravane passe.

```

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