Ops, forgot the tag last time.

Hi everyone,

I'm trying to use Timer 3 on the 18F8720 to count the number of pulses. I have a function generator connected to RC0 outputing a square wave, but am getting nothing.

Timer 3 is set up as below:

;***********************************************************************
; Timer 3 --  Used to count the count.
;***********************************************************************
 movlw B'00000110'   ; Timer 3 Off, No Prescale, Not Sychronised
 movwf T3CON     ; Ext input
 bcf IPR2,TMR3IP   ; Timer 3 low priority interrupt
 bsf PIE2,TMR3IE   ; Timer 3 Interrupt enable
 clrf TMR3H
 clrf TMR3L
 bsf T3CON,TMR3ON  ; Start Timer 3 (Count)


I'll try and describe what I'm trying to do here. I have a circuit outputting pulses, I want to count how many I get in 25ms. The max freq the pulses will be is 100kHz, so the 16 bit counter should never overflow. The interupt is there just incase something screwy happens and it does overflow.

So every 25ms I read TMR3L and TMR3H, then clear them, wait 25ms and read them again, forever! I currently have a function generator attached to RC0 putting in a square wave to simulate the circuitry. Every time I read TMR3L and TMR3H they are zero.


Have I done something stupid? Or missed something obvious? I've been trying to debug this all afternoon with no luck.

Thanks for any help,

Graham



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