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I believe I am having a problem with the pulse I am
sending to a servo connected directly to portb pin 3.
I have tmr0 set to overflow ever .0001 seconds. The
variable 'count' is incremented each time tmr0
overflows when count reaches 200 it is reset to 0.
When count is equal to zero I set portb pin 3 and when
count equals pw1 I clear the pin. I believe this
should give me a 1ms pulse every 20ms. This was not
working like I thought and I wanted to take a look at
the pulse so I downloaded one of those ocilloscopes
that runs through a sound card as I did not have
access to a real one. Well I found out that I am not
getting a nice square wave. The rising edge looks fine
but the falling edge is a slope. Can anyone tell me
how to correct this? I have included my code and also
attached an image I captured from the occiloscope.
Thanks.


LIST R=DEC

INCLUDE "p16f84a.inc"

CBLOCK 0x0C
_w
_status
_pclath
_fsr
count
pw1
ENDC

__CONFIG _CP_OFF & _WDT_OFF & _XT_OSC & _PWRTE_ON

push    macro
        movwf   _w                      ;Save registers
        movf    STATUS, w
        movwf   _status
        movf    PCLATH, w
        movwf   _pclath
        clrf    PCLATH
        endm

pull    macro
        swapf   _pclath, w
        movwf   PCLATH
        movf    _status, w      ;Restore registers
        movwf   STATUS
        swapf   _w, f
        swapf   _w, w
        endm

PAGE

        org             0
        nop

        goto    Main

        org             4                       ;Interrupt

        push

Timer0
        btfss   INTCON, T0IF
                goto    Iend
        movlw   165
        movwf   TMR0
        bcf             INTCON, T0IF
        incf    count
        movlw   200
        subwf   count, W
        btfss   STATUS, Z
                goto    Step1
        movlw   0
        movwf   count
Step1
        movlw   0
        subwf   count, 0
        btfsc   STATUS, Z
                bsf             PORTB, 3
        movf    pw1, W
        subwf   count, 0
        btfsc   STATUS, Z
                bcf             PORTB, 3
Iend

        pull

        retfie

Main

        bsf             INTCON, GIE
        bsf             INTCON, T0IE

        bsf     STATUS, RP0
        bcf             OPTION_REG, T0CS
        bsf             OPTION_REG, PSA
    bcf         STATUS,RP0          ; RAM PAGE 0

        movlw   156
        movwf   TMR0

        clrf    PORTB

        bsf     STATUS, RP0
        bcf     TRISA ^ 0x080, 1
        bcf     TRISA ^ 0x080, 2
        clrf    TRISB
        bcf     STATUS, RP0

        clrf    PORTA
        clrf    PORTB
        clrf    count

        movlw   10
        movwf   pw1

Loop
        nop
goto    Loop
end


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