[time-nuts] 1PPS to 32.768 khz
Tom Van Baak
tvb at LeapSecond.com
Wed Oct 19 13:10:55 EDT 2016
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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