Hi,

After much reading up, I found some registers related to timer1. 
Using my earlier (and finally successful) RS232 program, I tried to
send the contents of TMR1 every time a button is pressed.  When I
tried to send TMR1H (most significant byte), it was always d'8', and
the least significant byte was always changed around, starting at 85,
then after a few resets, 86, then 87, and finally 83.

I setup T1CON with:
00001011
and later tried
00001111

That's: system clock not running off tmr1, no prescaler (1:1), osc
enabled, I tried syncing on and off - no change, tmr1 source is
external, and tmr1 is on.

On 5/8/05, Olin Lathrop <olin_piclist@embedinc.com> wrote:
> Dave Turner wrote:
> > Firstly, I'm not running off battery power.  After much fiddling with
> > config bits I have discovered that with the PIC running on XT mode, it
> > runs a lot faster than it should if it is using the 32.768KHz clock.
> > Also, on INTRC mode it runs too fast.  On EXTRC, LP or HS mode it
> > doesn't run at all.
> 
> Sounds like general confusion about the system oscillator.  Get this figured
> out first, because everything else mostly depends on it.  If you're not
> running on battery power, why not run the PIC at its maximum clock speed of
> 20MHz?  All you need is a 20MHz crystal specified for parallel operation and
> two caps around 22pF, with the oscillator set to HS mode.
> 
> If the issues is pins or board space, then the internal oscillator is a good
> choice.  You can use it to run the PIC, and the timer 1 oscillator for
> accurate timing.
> 
> > The reason I'm trying to use the 32.768KHz clock as the system clock
> > is that I don't have a clue how to make a delay by checking a clock -
> > The only method I know is many embedded loops.
> 
> Fix this first.  Since you're willing to have a crystal anyway, I would make
> is a 20MHz crystal on the main oscillator.  Once you've done that, it's very
> easy to set up a periodic interrupt of 1mS, for example, using timer 2 and
> its period register.  This would happen once every 5000 instructions, so
> doesn't add much load to the processor.  As long as 1mS is close enough
> timing for everything else in the system, this will work fine.
> 
> Once you've got that, there are many ways to implement timers for longer
> periods.  One way is to have a counter for each delay event you need.  To
> wait, you set the counter to the number of mS to wait.  The interrupt
> routine decrements the counter whenever it's not zero, and sets a flag when
> it decrements it from 1 to 0.  Now the foreground code can go off and do
> other things, and the flag becomes just another event to handle in the main
> event loop.
> 
> That's only one of many ways to do this.
> 
> 
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