Mark Willcox wrote:
>
> Hi all
>   I would like to build a simple stopwatch using a 16f873 @ 4Mhz(xt). The
> stop/start could be on RA4/TOCS or an external interrupt on RB0. Once
> started, I would like the counter to incf a register(s)each FF to 00
> overflow and count the number of overflows during run time(# of overflows x
> machine cycles = ms or sec)? I would like this stopwatch to be able to count
> from milliseconds up to seconds(if possible). I would like to display the
> count register(s) total at the end(stop) of count on ports B&C(2 x 8 LED
> bargraphs). Any help you can give will be greatly appreciated, thanks in
> advance, Mark
> ________________________________________________________________________
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Got no idea if it works properly.

Key press on PORTA,0 reads and sets data on PORTB,C.

        include "P16f873.inc"

        CBLOCK 0x20

TimeH
TimeL
Debounce
KeyFlag

        ENDC

        org 0h

        clrf PORTA
        clrf PORTB
        clrf PORTC
        bsf STATUS,RP0
        movlw b'11000010'
        movwf OPTION_REG
        movlw b'00000001'
        movwf TRISA
        clrf TRISB
        clrf TRISC
        movlw b'10000110'
        movwf ADCON1
        bcf STATUS,RP0

        clrf Debounce
        movlw b'00000001'       ; flag key is up
        movwf KeyFlag
        clrf TimeH
        clrf TimeL

Reset   movlw 84h
        movwf TMR0
        bcf INTCON,T0IF

WtLoop  btfss INTCON,T0IF       ; 1mS @ 4MHz
        goto WtLoop

        incf TimeL
        btfsc STATUS,Z
        incf TimeH

        movf Debounce
        btfsc STATUS,Z
        goto ButtChk

        decf Debounce
        goto Reset

ButtChk btfss PORTA,0   ; test for low
        goto IzLow

        btfss KeyFlag,0
        goto Reset      ; already pressed

        bcf KeyFlag,0   ; flag key is down
        movlw 10h
        movwf Debounce

        movf TimeH,w    ; output data to PortB & C
        movwf PORTB
        movf TimeL,w
        movwf PORTC

        clrf TimeH      ; reset timers
        clrf TimeL
        goto Reset

IzLow   btfsc KeyFlag,0
        goto Reset      ; already released

        bsf KeyFlag,0   ; flag key up
        movlw 10h               ; just pressed
        movwf Debounce
        goto Reset


        end
--
Best regards

Tony

http://www.picnpoke.com
mailto:sales@picnpoke.com