[time-nuts] GPS message jitter (was GPS for Nixie Clock)
scott.j.stobbe at gmail.com
Tue Jul 19 14:48:39 EDT 2016
Very true. If your exchanging data for loose timing purposes (wall clock)
over a UART whether it is binary coded or ASCII coded is immaterial. You
will always introduce at least 1/16 of a bit time of jitter, if not one
full bit time, allowing the uart to sync to start bit edge.
In full honesty I have never read the official NMEA-0183 specification.
Just a sample from an unoffical NMEA0183.pdf
*ZDA Time & Date – UTC, Day, Month, Year and Local Time Zone*
So for a GPS or a timing unit on a NMEA-0183 bus, do they report their best
estimate of time to the nearest 10ms when the packet is sent? (since a PPS
line isn't shared)
On Tue, Jul 19, 2016 at 1:17 PM, Chris Albertson <albertson.chris at gmail.com>
> On Mon, Jul 18, 2016 at 10:44 AM, Scott Stobbe <scott.j.stobbe at gmail.com>
> > I am happy to hear you issue was resolved. What I meant to say is the
> > problem could also be mitigated using the UART's flow control, this could
> > be done by the original GPS designers or by an end user if the CTS line
> > pined out.
> The original GPS designers where sending NMEA-0183 data out to devices
> that accept and use NMEA data. GPS was not the first to work with
> NMEA. Lots of other instruments also output NMEA. I doubt they ever
> would have envisioned people using NMEA data for precision timing.
> Typically if you want to do precision timing you's use a GPS that
> outputs some binary data format. NMEA-0183 does not have flow control
> Chris Albertson
> Redondo Beach, California
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