[time-nuts] 1PPS to 32.768 khz

Tom Van Baak tvb at LeapSecond.com
Wed Oct 19 13:10:55 EDT 2016

David, Hal,

When I did the PIC divider I first tried the normal phase accumulator (DDS) approach. But I couldn't fit it in 38 instructions. So that's why I went with the binary leap year-like approach instead. The code, and very detailed comments are at:

Note this chip, like most of my PIC dividers, is drop-in compatible with the TAPR TADD-2 mini board:


----- Original Message ----- 
From: "Hal Murray" <hmurray at megapathdsl.net>
To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Cc: <hmurray at megapathdsl.net>
Sent: Wednesday, October 19, 2016 3:29 AM
Subject: Re: [time-nuts] 1PPS to 32.768 khz

> davidwhess at gmail.com said:
>> I think a PIC might be fast enough to DDS it.  The output bandpass filter
>> will cure a lot of sin.  Using a dedicated switched capacitor filter would
>> be fun but more expensive. 
> There are two parts to a DDS like setup.  One is the math for the DDS and 
> then spining for the right number of cycles.  The other is a PLL to measure 
> the speed of the clock driving the CPU and tweaking the DDS "constants" so it 
> tracks the PPS.  It might be fun to do that with a fixed number of cycles.  
> Or maybe you can use a counter/timer to count cycles.
> You don't need any filtering.  The goal is not to make a pretty picture on a 
> spectrum analyzer.  All you have to do is get the long term timing right so 
> the clock doesn't drift.
> -- 
> These are my opinions.  I hate spam.

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