Hi The Shera counter is not running in the same fashion you would be running an input capture pin.
Bob On Dec 6, 2012, at 8:45 PM, David <[email protected]> wrote: > Sorry. The Shera counter is 16 bits and not 12 bits but that does not > change what I posted. > > On Thu, 06 Dec 2012 19:17:48 -0600, David <[email protected]> > wrote: > >> It is not a 16 bit capture and it does not run at 1/4 the clock rate. >> >> The Shera uses a 12 bit counter to capture the phase difference >> between the OCXO frequency divided by 16 and GPS pulse per second >> output to a resolution of about 42ns. >> >> What I suggested effectively captures the same phase difference but >> divides the OCXO by 65536 and only has a resolution of 100ns. The >> OCXO division is just conceptual though as it comes from the 16 bit >> timer/counter overflow internal to the microcontroller so in practice, >> the timer/counter is arbitrary length with an interrupt about every >> 6.5ms doing the housekeeping for the extra bits. It directly measures >> the pulse per second period to a resolution of 100ns using the OCXO as >> a clock. If a 20 MHz OCXO was used (limited by the maximum clock >> frequency of the microcontroller), then the resolution would be 50ns. >> >> That is not how I plan on designing my own GPSDO which has taken a >> significant turn from what I posted about here some time ago but I >> have stopped discussing that until I have some results to share. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
