[time-nuts] ANFSCD - Synchronizing time in home video recorders
azelio.boriani at screen.it
Thu Feb 2 16:18:21 UTC 2012
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:
> ----- 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
> 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
>> -----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
>> I think I've seen comments about making 32 KHz from 10 MHz in a PIC or
>>> tvb has this web page, but I don't see a 32 KHz option:
>> 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.
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