[ntp:questions] Reasons of NTP not to use GPS source

William Unruh unruh at invalid.ca
Wed Apr 9 22:01:00 UTC 2014


On 2014-04-09, E-Mail Sent to this address will be added to the BlackLists <Null at BlackList.Anitech-Systems.invalid> wrote:
> On 4/8/2014 2:57 PM, William Unruh wrote:
>> On 2014-04-08, <a.everett.000 at gmail.com> wrote:
>>>
>>> Also, as previously mentioned,
>>>  simply feeding a 3.3V or 5V pps output from a GPS receiver
>>>   into a RS232 port will not work as the voltage levels are different.
>>>  You will need a simple TTL logic to RS232 converter such as a MAX232
>>>   device to convert the PPS output signal to the correct voltage level.
>>>
>> Actually false form most serial ports these days. While the standard
>> says 5V the actuallity is that 3,3 V will trigger it on almost all
>> serial ports. Ie, in general it is a non-issue. Note that the fact that
>> serial and parallel ports and their interrupts are disappearing from
>> almost all computer is probably a bigger problem.
>
> The current version is TIA/EIA-232-F (circa 1997, last updated 2002?)

And this is irrelevant. The question is not what the standard says but
what the serial ports actually handle. Again, does anyone know of a
serial port which does NOT handle TTL logic imputs?


><BlockQuote>
>  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.
>   This effectively gives a 2-V minimum noise margin at the receiver.
></BlockQuote>
>
> I've used some current TI (RS232-F speced),
>   that don't switch if the voltage remains positive;
> However I have also used some current Maxium that switch at ~ 1.5 V.
>
>  I haven't really seen this change much in the last two years,
>   however I certainly could be missing out on some modern chipset's RS232 features.
>
>



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