[time-nuts] DS3231m 1HZ output stability

d0ct0r time at patoka.org
Wed Feb 26 15:26:51 UTC 2014



To answering myself: I think nothing wrong with DS32XX. I hooked up GPS 
1PPS output to the same timer (different channel) where I have 1PPS from 
RTC. Now I see something like this.

# Delta GPS: 7330, Delta RTC: 7330
# Delta GPS: 7330, Delta RTC: 7329
# Delta GPS: 7330, Delta RTC: 7329
# Delta GPS: 7330, Delta RTC: 7330
# Delta GPS: 7330, Delta RTC: 7330
> # Delta GPS: 405, Delta RTC: 705
> # Delta GPS: 405, Delta RTC: 705
# Delta GPS: 7330, Delta RTC: 7330

Definitely something wrong with my code or the way how MCU handle 
different events (interrupts).

Reggards,

V.P.



On 2014-02-25 17:32, Tom Van Baak wrote:
>> I would like to ask if somebody did measurement for that Dallas DS32XX
>> series chips. Is that 1PPS (1HZ square wave) stable there or it has 
>> some
>> issues ? I am thinking that "burp" in my tests could be because of my
>> poor code or may be because of DS32XX doing temperature conversion 
>> every
>> second, which cause an impact to the 1HZ output. I would be interested
>> to hear any information about. From the datasheet of DS3231m , that 
>> 1HZ
>> from DS32XX should be stable.
> 
> Both the GPS and DS32XX 1PPS should be fine. Are your free-run
> counters really free? It looks like a simple bug in your code.
> 
> All this is very easy to debug if you have even the most basic
> frequency or time interval counter available to independently validate
> the GPS or the DS32XX 1PPS interval.
> 
> /tvb
> 
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-- 
WBW,

V.P.



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