Hi again:

It was my problem getting confused about counting from 0 or counting from 1.
In code below should be:

   movlw    .250    ;    count 0 to 250 for 10, 5, 1 MHz

I had an offsetting error in the 8 ms tick counter.
Precision Clock 3 web page:
http://www.pacificsites.com/~brooke/PRC68COM.shtml#PC3

Have Fun,

Brooke Clarke

Hi:

I'm using Timer 2 as an 8 ms tick interrupt clock.  The 16F88 gets it's 
external clock from a 1.00000000000000 MHz source.  But after running 
for 20 hours the clock is 4 to 5 seconds fast.  Any ideas why?  Timer 2 
is setup:

;  Fin  Fclk     Pre  Cntr  Freq    Post    Int Hz    Int ms
;  1M   250k     4    250   250     2       125       8  

   banksel T2CON
   movlw    0x0D    ; 2 post, Cntr On, 4 Pre: 1 MHz in
   movwf    T2CON
   banksel PR2
   movlw    .251    ;    count  to 250 for 10, 5, 1 MHz
   movwf    PR2
   banksel PORTA

The mid range reference manual says that after TMR2 gets to PR2 it's 
reset to FF and the 16F88 manual says it's reset to 0.  Ten minutes of 
running shows that PR2 needs to be set to .251 not the 250 that seemed 
correct.  I like the idea that the counter gets automatically reset.  In 
a prior clock using Timer 1 it was a hassle to load the registers and 
keep track of the latency, but it did work.

Have Fun,

Brooke Clarke

-- 
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w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
http://www.precisionclock.com


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