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I'm certainly no expert, but it looks like a classic capacitor discharge issue to me.  If you have a cap on this output, it will take time for it to discharge causing the slow decay in voltage instead of a nice sharp corner.  I can't see your circuit but do you have a cap connected across the pin you measured with the scope?
>
> From: Joel Middleton <chopsuey1973@YAHOO.COM>
> Date: 2003/06/15 Sun AM 01:21:50 EDT
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [PIC]: Servo Pulse Problem
>
> 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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