Re: x10 - CM12U (CM11) Clock Accuracy

[Charles Sullivan <cwsulliv@xxxxxxxxxxxx>]

On Tue, 25 Sep 2007 21:47:07 +0100, Martin Davies wrote:

> Hi -
>
> Thanks for this. Do I understand from your message that the CM11/12 uses the
> mains supply frequency to regulate its internal clock? If so I may have a
> problem as we are connected to a private generator supply and the frequency
> does vary somewhat. Even so the variation in frequency doesn't account for
> the large errors I'm experiencing with timed events. Other postings (c.f
> http://www.idobartana.com/hakb/) talk about a modification to the internal
> clock to improve its accuracy but this doesn't seem to apply to the CM12U as
> it doesn't have an 80C48 chip.
>
> I would appreciate hearing of any ideas for improving clock accuracy?
> Thanks.

The post cited refers to the CP290 (an antique), not the CM11A.
They're two entirely different beasts, not just in the clock.
The CP290 used a crystal oscillator which could be improved; the
CM11A/CM12U uses the AC mains frequency, which you're generally
stuck with.

Does your CM12U gain time or lose time?  If it gains time (runs
fast and timers execute earlier) it's possible that excessive
noise or spikes on the generated AC waveform could cause it to
do that, in addition to whatever changes are due to fluctuation
in the mains frequency.