[time-nuts] Fwd: M12+T ASCII interface - I'm confused?

Chuck Harris cfharris at erols.com
Thu Nov 20 10:33:46 EST 2008


Stephan Sandenbergh wrote:
> Hi,
> 
> Now I'm slightly confused:
> 
>>> My gut tells me that  <Checksum><cr><lf><@><@> would be believable more than
>>> say 95% (if not 99%) of the time. I've got the following observations:
> 
> In the above I assumed no data length checking is employed.
> 
>>> - 95% is a bad number in accurate timing applications.
>> You misunderstand. You can get as close to 100% as you
>> want. Some of us have logged data from M12+ receivers without
>> error for weeks or months -- gigabytes, error-free.
> 
> Sure, I assume you refer to the case when you check the data length as
> well? I meant that the <Checksum><cr><lf><@><@> byte string could also
> potentially exist in the data itself, but only in very rare cases
> (from there the 95% thumb suck).

No it cannot.  It would be:<checksum><cr><cr><lf><lf><@><@><@><@>...

As I understand it, they use a byte stuff code, where any of the "special"
bytes must be doubled if they are in the data.... And, there must be a
data area length check or you could get into some truly pathological situations.

-Chuck Harris




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