piclist 1999\10\13\051409a >
Thread: Clock Accuracy
picon face BY : Russell McMahon email (remove spam text)

>What sort of accuracy does one get with various clocks (not including RC)
>for a PIC? For MIDI serial, the specs call for 1% timing accuracy. What
>of difficulty will there be in getting a clock to this accuracy?

A resonator will easily meet these specs.
Murata and others provide details on web.
Off the cuff resonators give you about 0.1% across temperature and crystals
are 10+ times better across temperature.


> Is there
>any difference in accuracy (or other specs) between a resonator and a
>crystal (or diff. types of crystal?

Cheapest available "microprocessor crystals" will be entirely adequate.
Resonators are (usually) cheaper and can eliminate 2 external capacitors.
Murata have had good feedback on this list as being responsive to customer
needs and understanding specific microprocessor oscillator circuit demands.

What about higher accuracies? What is
>the maximum (practical) achievable accuracy (i.e. in production, not like 1
>in a 1000 will get it) for various High speed clocks? What about driving
>multiple PICs at reliable high speed, anything good for this (be nice not
>have to redesign the circuit when another PIC (and hence load
>resistance\capacitance\inductance) are added?

You should be able to get essentially 100% compliance at this (low) accuracy
What do you mean by "high speed"
Changes in crystal parameters can make a particular capacitor/microprocessor
combination suddenly not work. However, any crystal manufacturer worth their
salt will be able to guarantee to meet a prior spec given a sample and
circuit description.

Try Rakon for starters. AFAIK they were originally a NZ based firm but they
now supply some very smart crystal based products worldwide to some very
large users. There are many many more reputable suppliers.

     Russell McMahon

>From another world - http://www.easttimor.com

What can one man* do?
Help the hungry at no cost to yourself!
at  http://www.thehungersite.com/

(* - or woman, child or internet enabled intelligent entity :-))

-----Original Message-----
From: Thomas Brandon <tomSTOPspamspamEraseMEPSY.UNSW.EDU.AU>
Date: Wednesday, 13 October 1999 12:58
Subject: Clock Accuracy


<04b201bf155a$73065ce0$373061cb@mkbs> 7bit

See also: www.piclist.com/techref/timers.htm?key=clock
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