I'm currently a bit confused and I hope someone can straighten my
confuseness out.

My question is about clock-selection (crystal, RC or resonator). I've
read here and there that if timing is not crucial, it does not matter
which type I choose - an RC-clock will be fine. However, if I need
accuracy, I should pick a crystal.

This is my scenario: I've built a kind of chess-clock using a
32768Hz-crystal as Timer1-oscillator. The device is able to measure up
to 90 minutes of time, that is - this is the longest measured period
the device should be able to handle. I'm not interested in uS-accuracy
- some 1ms clock-drift is not fatal - but I don't want 2 seconds
drifting. You probably get the idea.

Will an RC-setup do, or do I need an xtal for accurated oscillation?


Also, is there any rule of thumbs regarding the branding of xtals?
I've got these ones in my junkbox:

http://bos.hack.org/tmp/cache/xtals/small.jpg
http://bos.hack.org/tmp/cache/xtals/large.jpg

Only two of the large ones are labeled "MHz". If the Hz-mark is gone,
can I assume it's MHz? Or does it differ between manufacturers?  I
would prefer using one of the small xtals I have rather than using the
large ones or buying new ones, because 1) the project budget is
breached already and 2) the prototype board will not fit a large xtal
without jumpering (i.e. clutter the board down).


-- 
- Rikard - http://bos.hack.org/cv/
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