Hi everyone,

Need some help on the source code below. Basically i need to implement
a counter using the Timer0. I am using a 16F84A and i disabled the
watchdog. I am assigning the ratio 1:256 for the prescaler and
i am using additional 2 counters.

; source codes

MAIN    < some operation >

        bank1
        bsf     OPTREG,RBPU
        bsf     OPTREG,INTEDG
        bcf     INTCON,INTF
        bsf     INTCON,INTE
        bsf     INTCON,GIE

LOOP    sleep           ; let IRQ wake it up and determine functions
        nop
        clrwdt              ; initialisation of Timer0
        bank1
        bcf     OPTREG,PSA
        bcf     OPTREG,TOCS
        bsf     OPTREG,PS2
        bsf     OPTREG,PS1
        bsf     OPTREG,PS0

        goto    DATA_RECEIVE

FINISH  goto    LOOP    ; go back to sleep and wait for the next INT


DATA_RECEIVE
        clrf    timer2
        clrf    timer3
DV_HIGH bank0
        btfss   PORTB,DV   ; TEST FOR THE DV ( / Data Valid )
        goto    DV_LOW     ; if Low, then Data Valid True, branch out

        btfss   INTCON,TOIF     ; if not,check if TMRO overflow
        goto    DV_HIGH         ; no overflow, check DV again
        bcf     INTCON,TOIF     ; got overflow, reset the TOIF
        incf    timer2          ; increment timer2 counter
        btfss   STATUS,C        ; check if timer2 overflow
        goto    DV_HIGH         ; timer2 no overflow, check DV again
        clrf    timer2          ; timer2 overflow, reset timer2
        incf    timer3          ; increment timer3 counter
        movf    timer3,W
        sublw   H'0A'           ;
        btfss   STATUS,Z        ; check for timer3 = 10
        goto    DV_HIGH      ; timer3 less than 10, continue check DV
        goto    LOOP            ; timer3 = 10, stop checking DV
                                ; go back sleep


The accuracy of the time is not important. and based on a rough calculation
the duration that i can wait for DV ( Data Valid ) to go LOW is around

time for TMRO to overflow

(1 / 2.5MHz) x 256 x 255 = 0.02611 sec

time for timer2 to overflow

0.02611 sec x 255 = 6.658 sec

time for timer3 to overflow ( the whole duration )

6.658 sec x 10 = 66.58 sec

What i am trying to do is to have a counter so that if the DV
does not goes LOW after around 1 min. , i stop polling for DV
and return to sleep. actually the DV is some sort of user response.
is there anything wrong with my code? One last question, can i just simply
reset the TMR0 flag as and when i like it? and when the overflow occurs, the
timer will still continue running right?

Thanks for reading.


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