[ntp:questions] Fwd: Re: NetBSD GPS/PPS using 4.2.6p3

A C agcarver+ntp at acarver.net
Wed Aug 24 01:25:06 UTC 2011


On 8/23/2011 15:27, unruh wrote:
> On 2011-08-23, Uwe Klein<uwe at klein-habertwedt.de>  wrote:
>> unruh wrote:
>>> But from his test, his system is labelling both edges.
>>>
>> so he has bounces on the line?
>>
>> either that or rise/falltime is so low and noise so high
>> that receiver hysteris is not sufficient to  supress multiple
>> HL/LH changes?
>
> No, his test shows that the line changes and then 100ms later it changes
> back and 900ms later it changes again (ie once per second it rises and
> falls.) Ie, it is behaving exactly as it should if it were detecting a
> pulse 100ms long.It is detecting both the rising and falling edge.

I just checked and the pulse is almost exactly 100 ms low going and 900 
ms high (within about 1 ms) so it's 90% duty cycle high most of the time 
with a swing low.  The signal itself is clean down to microvolt levels. 
  The total voltage swing is about 12 volts (which would stand to reason 
since I'm feeding the TTL level PPS output of the GPS board through one 
channel of a MAX232 level shifter).

Therefore the machine is receiving a nice, clean PPS signal on DCD (DCD 
pin was also verified yet again and is correct by hardware specifications).



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