[time-nuts] 10 MHz to 32.768 kHz converter

Martyn Smith martyn at ptsyst.com
Sun Mar 20 14:26:16 EDT 2016


Hello,

 

First of all quick apologies for sending an email last week without deleting all the old information from previous postings.  

 

I have been playing around with producing 32.768 kHz from 10 MHz using a PIC chip.

 

I  have a real time clock calendar chip that requires a 32.768 kHz crystal.  I want to feed it with 10 MHz signal instead, so it is synchronised to my main 10 MHz in a frequency standard I am designing.

 

The method I’m using has been documented before where we have two loops running 9632 times through a 39 instruction loop and 
55904 times through a 38 instruction loop, each time toggling the output pin.

 

I have done this and am getting approximately 32.768 kHz with the FM modulation as described by previous authors.

 

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)?

 

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

 

Does the actual model of PIC chip influence the accuracy?

 

Regards

 

Martyn

 

 

 



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