[ntp:questions] Very large jitter and offsets on GPS ref clock after upgrade to "p5"

unruh unruh at invalid.ca
Fri Jan 6 22:23:21 UTC 2012


On 2012-01-06, E-Mail Sent to this address will be added to the BlackLists <Null at BlackList.Anitech-Systems.invalid> wrote:
> On 1/6/2012 12:28 PM, unruh wrote:
>> Eg, your encore pluse is a TTL level pulse (0-3 volt transition)
>
> I thought he indicated he had a Oncore UT+ ?
>
>  The M12M Oncore specs TTL interface (0 to 3 V)
>  The UT Plus Oncore TTL specs TTL interface (0 to 5 V)
>  The GT Plus Oncore specs TTL interface (0 to 5 V)
>
>
>> standard for serial ports is basically -5 to +5 volt transition
>
> The RS-232 standard (currently TIA/EIA-232-F)
>  {normalized with ITU-T V.24, V.28, and ISO/IEC 2110}
>
> Electrical Specification:
> "A logic 0 is represented by a driven voltage between 5 V and 15 V
>  and a logic 1 of between ?5 V and ?15 V."
> "At the receiving end, a voltage between 3 V and 15 V represents a 0
>   and a voltage of between ?3 V and ?15 V represents a 1.
>   Voltages between ?3 V are undefined and lie in the transition region."
>
>
> Looks like a M12M would be unreliable without an additional RS-232 driver,
>  even more so over a long cable.

iAs I understand it, almost all serial ports actually accept something
 between about -25 and
+1 or 2 volts as "1" esp on the control lines so that they can in fact
operate with TTL logic. But there is no guarentee, and some serial ports
might not. It does not have to in order to meet the standards. 
 He migh have one that does not or rather is marginal around 0. and sees
say 0 to 25 as 0 and -25 to 0 as 1 with 0 being somewhat ambiguous. 
All I was saying was that it IS possible that pulses are being missed. 
He should not rule that out as a possible reason for his problems. 

. 
>



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