[time-nuts] ANFSCD - Synchronizing time in home video recorders

[Azelio Boriani]

Yes, shortly after having sent out the message I realized that I was, as
usual, too fast. I'm aware that a simple microprocessor can't be used but a
Spartan3 can be involved. Then another problem: the 2.048MHz is about 1/5
of the 10MHz so it is not possible. Sofar the way out is: dividing the
10MHz by 625 and then multiplying by 128 using the DCM in the Spartan3...
but nothing clever in this method. Sorry, not a valid contribution.

On Thu, Feb 2, 2012 at 6:07 PM, Tom Van Baak <tvb at leapsecond.com> wrote:

> Azelio,
>
> 2.048 MHz has a cycle period of just 488.28125 ns so a PIC/AVR is (far)
> too slow to use the same trick I did on the low frequency 32 kHz.
>
> I think you'll have to use a PLL for that one. How about a 16 kHz compare
> rate: 10 MHz / 625 = 16000 Hz = 2.048 MHz / 128
>
> /tvb
>
>  ----- Original Message -----
>  From: Azelio Boriani
>  To: Tom Van Baak ; Discussion of precise time and frequency measurement
>  Sent: Thursday, February 02, 2012 8:18 AM
>  Subject: Re: [time-nuts] ANFSCD - Synchronizing time in home video
> recorders
>
>
>  Amazing... there is always something to learn from TVB. Now I'll try to
> derive a 2.048MHz G.703-13 clock from a 10MHz clock. I suspect that the
> procedure is similar, even if 2048KHz is not quite a power of 2.
>
>
>  On Thu, Feb 2, 2012 at 4:35 PM, Tom Van Baak <tvb at leapsecond.com> wrote:
>
>    Hi Roberto,
>
>    The motivation for this, I assume most list members know, is to
>    drive cheap quartz stepper motor clocks with precise 32 kHz
>    frequency, one derived from an atomic or GPS 10 MHz.
>
>    The 10 MHz to 32 kHz PIC divider I wrote uses a sort of binary
>    "leap year" algorithm to adjust the digital output phase to be as
>    close as possible to the ideal 32.768 kHz phase on each cycle
>    and also to have zero long-term error.
>
>    I'm not sure how well a multi-level leap year algorithm relates
>    Breseham's algorithm. I tracked down his 1965 plotter article.
>    There might be common ground there.
>
>    With non-integral ratios like this case, or without external analog
>    components (e.g., PLL), it seems some level of jitter is always
>    unavoidable. So the goal was to make it as mathematically small
>    as possible, and furthermore, to be able to do the math within a
>    half cycle, which is only 15 microseconds.
>
>    I'll send you an early draft of the PIC code; the version that was
>    most clear before I had to pinch too many cycles and added too
>    many features. Let me know what you think.
>
>    I also simulated the algorithm on a PC and measured the ADEV
>    and phase noise. That simulation code is file 10m32k.c under:
>
>    http://www.leapsecond.com/tools/
>
>    /tvb
>
>    ----- Original Message ----- From: "Roberto Barrios" <rbarrioss at msn.com
> >
>    To: "Tom Van Baak" <tvb at leapsecond.com>; "Discussion of precise time
> and frequency measurement" <time-nuts at febo.com>
>    Sent: Thursday, February 02, 2012 5:09 AM
>    Subject: Re: [time-nuts] ANFSCD - Synchronizing time in home video
> recorders
>
>
>
>      Hi Tom,
>
>      I'm interested in that divider. Actually, insterested in knowing how
> it works, not in the .HEX file.
>
>      Breseham's algorith works but has inherent jitter and I've found no
> other solutions for situations like that.
>
>      I'd live to know how it is done.
>
>      Thank you,
>      Roberto EB4EQA
>      http://www.rbarrios.com
>
>
>      -----Mensaje original----- From: Tom Van Baak
>      Sent: Thursday, February 02, 2012 10:34 AM
>      To: Discussion of precise time and frequency measurement
>      Subject: Re: [time-nuts] ANFSCD - Synchronizing time in home video
> recorders
>
>
>        I think I've seen comments about making 32 KHz from 10 MHz in a PIC
> or AVR.
>
>        tvb has this web page, but I don't see a 32 KHz option:
>         http://www.leapsecond.com/pic/picdiv.htm
>
>
>      Hal,
>
>      Yes, I have a PIC divider that takes 5 or 10 MHz input and
>      outputs a 32.768 kHz square wave with minimal jitter and
>      no long-term phase offset. Contact me off-line if interested.
>
>      /tvb
>
>
>
>
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