> > Any pointers to good tutorials / examples about using a non-system
> > clock for a 1 second delay would be extremely welcome.

If you're going to use a 32768 xtal on TMR1 -

32768/4 = 8192Hz incrementation rate (DS30487B, Section 7.1)

Therefore, re-load TMR1 with 0x0000-0x2000 = 0xe000 (=
- d8192) or just re-load TMR1H with 0xe0, as TMR1L has
already gone through 0x00. When TMR1 counts up from 0xe000
to pass through 0x0000 you can either have it generate an interrupt
(by enabling TMR1IE) or poll TMR1IF to see if it's set. In either
case, clear TMR1IF and reload. This is a very simple background
1 second timer. You don't need to do anything other than note that
TMR1 has gone through 0x0000 (and of course re-load it before
TMR1L gets to 0x00 again). Using binary counting like this means
you don't have to worry about reload jitter that can happen when
loading the timer low byte with non-zero values

You can work out the maths if you're using a different xtal as the
main oscillator and using another timer and/or pre-scalers

I'd go along with Byron about using mains cycles as the primary
timing source (RA4/T0CKI - RB0/INT - RB6/T1CKI). Note
though that mains frequency varies slightly during the day due to
demand and you should look at the daily (ie a 24h period) count
for accurate timing. IOW, the number of mains cycles coming in
between 7am and 7pm is more than likely going to be be less
(frequency would be 49.xx or 59.xx Hz) than the period 7pm to
7am (frequency will be catch-up 50.xx or 60.xx Hz)

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist