Hi PSoC's are another attractive possibility that suffers from the same basic "re-clock everything" flaw. Lots of time down the drain there….
Bob On Dec 6, 2012, at 8:22 PM, [email protected] wrote: > David, > > The NXP LPC932 processor series are very cheap and small, and we got very > excited to see timers running at up to 32MHz internally if I remember > correctly. > > Then setting up a test system we noted that the timer can capture with > 32MHz resolution which is good enough for a low-cost GPSDO implementation, > but > that they gated the input pin through a flip-flop running at CPU core > speed, which was around 6MHz if I remember correctly. > > DAAHHHH. So all that fast timer resolution goes out the door by gating the > input pin instead of using non-gated inputs for the timer functions. > > It does work however, in the end we made that processor do the chores in > our quite old and discontinued FireFox GPSDO circuit. TVB has some plots on > his website for that unit I think, and its quite surprising what type of > stability we achieved with that little 8 bit bugger back then. > > bye, > Said > > > In a message dated 12/6/2012 16:00:27 Pacific Standard Time, > [email protected] writes: > > You can use the ATmega328 16 bit timer/counter in input capture mode > to count the number of 10 MHz OCXO cycles per pulse per second period > to a resolution of 100ns but there are some problems: > > The ATmega328 16 bit timer/counter external clock is limited to 1/4 of > the CPU frequency with an asynchronous source so the 10 MHz OCXO would > need to be divided down which would further limit performance and > require an external divider. Modifying the Aruino board to use the 10 > MHz OCXO in place of the CPU clock solves that problem. > > Then operating the counter/timer in input capture mode with the GPS > pulse per second signal connected to the input capture pin would allow > almost Shera like performance. The timing resolution would be 2.4 > times lower (and not asynchronous) limiting performance over short > time spans. > > _______________________________________________ > 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.
