[time-nuts] 10 MHz to 32.768 kHz converter

Hal Murray hmurray at megapathdsl.net
Sun Mar 20 21:36:36 UTC 2016


martyn at ptsyst.com said:
> My question is should I expect exactly 32.768000000 kHz (obviously assuming
> we use the same 10 MHz to drive the divider and all test equipment)?

Yes, as long as you are feeding the same reference to your counter and your 
divider you should get an exact answer.

> The closest I can get the 32.768 kHz is within about 0.1 Hz.

How accurate is your counter?

Do the arithmetic and count cycles.  You may be able to figure out how many 
cycles you are off.  You can try different chunks of code to verify that they 
are doing what you expect.  Or put trigger a scope on a PPS and see if the 32 
KHz is drifting.

> Does the actual model of PIC chip influence the accuracy?

Compare the cycle counts on the instructions.  I expect them to be the same, 
but I haven't compared various PIC versions in a long time.



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