Hi, I'm playing about with a PIC18F452 and trying to design a very
simple clock circuit, to show both UTC and Sidereal (astronomical) time
on a 2x16 LCD display. Before I start writing code using the C18
compiler, I'd like to ask for opinions for crystal frequencies that
'make sense' in a clock application. I was kindof expecting that a power
of 2 crystal such as 32768 khz or better still, a 4.194304 Mhz crystal
would be sensible, as the frequency is easily divisible into 1hz. But,
then, reading up about the TIMER0/1/2/3 modules, I begin to doubt that
it matters at all, since I can load a counter value appropriate to the
xtal, and have the counter overflow, and generate an interrupt, say
every 100'th of a second.

Is my understanding correct, that using TIMER0, accurate time can be
generated from any abitrary clock frequency?

I noticed that TIMER0 (and also TIMER1) have the ability to be clocked
independently from the CPU clock, from a 32768 khz watch xtal, is there
any reason for this, in terms of clock applications?  Would it be the
case that the 32768 khz xtal might be used when the main CPU clock had
been selected for ease of generating serial (RS232?) baud rates?

Sorry for all the questions.... steep learning curve for me right now...

Peter Moreton

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