[time-nuts] 10 MHz to 32.768 kHz converter

Vlad time at patoka.org
Sun Mar 20 18:23:18 EDT 2016



How about Bresenham's Algorithm to alternate imperfect periods to 
produce an average that matches any "perfect" period.

Refer to Bob Ammerman work to use Bresenham-type system for PIC MCU. He 
was using the counter works in the background, either by polling or 
Interrupt-Driven. So, the "SuperCycle" continues to run. The timer count 
the value is stored in a 3-byte register that is decremented by the 
software.

Regards,
Vlad

On 2016-03-20 14:26, Martyn Smith wrote:
> 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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-- 
WBW,

V.P.


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