Your duty-cycle technique sounds like it should give you what you expect =
since=20
I use the same technique to vary LED brightness.  I played with servos in=
 the=20
past, and did not have this problem.  Have you tried separating the PIC c=
kt=20
from the servo to isolate the problem?  If you have an oscope, put a smal=
l=20
load resistor at the output instead of the servo and see what you get the=
n. =20
If clean, then the servo is causing the problem, and you could try swappi=
ng=20
for another.  If you still get that decay pattern, you have PIC problems.=
 =20
Try another port or PIC.

Cheers,
-Neil.



On Sunday 15 June 2003 09:55, rneel@COX.NET scribbled:
> I'm certainly no expert, but it looks like a classic capacitor discharg=
e
> issue to me.  If you have a cap on this output, it will take time for i=
t to
> discharge causing the slow decay in voltage instead of a nice sharp cor=
ner.
>  I can't see your circuit but do you have a cap connected across the pi=
n
> 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=3DDEC
> >
> > 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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