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

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Wed Apr 9 03:19:07 UTC 2014

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?)
 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.

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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