3 channel PWM with customize duty cycle

[photoelectric]

hi,

long time no see

after many times checking on my pwm using osiloskope, i found out that the pattern of the pwm isnt fixed according to the lookup table value while the PIC is running.
this definitely affecting my inverter output and produce too many harmonics..
as you can see for the attached file:

both screen shot should have same length and pattern of pwm but when the PIC is running, the PWM seem keep expanding and de-expanding repeatedly thus changing the pattern.

sumting wrong with the codes or my osiloskope resolution??i dont think so

ClearWDT
DEFINE OSC 20
Phase       VAR BYTE[3]       ' Array used as pointers into lookuptable.
DutyCycle   VAR WORD[3]       ' Array storing the dutycycles retreived from the table
Temp        VAR WORD          ' Temporary variable to avoid hard to understand array indexing
i           VAR BYTE          ' General purpose counter
TRISC.2 = 0                   ' Set PORTC.2 (CCP1) to output
TRISC.1 = 0                   ' Set PORTC.1 (CCP2) to output
TRISB.5 = 0                   ' Set PORTB.5 (CCP3) to output
CCP1CON = %00001100           ' Set CCP1 to PWM 
CCP2CON = %00001100           ' Set CCP2 to PWM
CCP3CON = %00001100           ' Set CCP3 to PWM
T2CON = %00000101             ' Turn on Timer2, Prescale=4
PR2 = 249                       ' Set PR2 to get 5KHz out
ADCON1 = 7                      ' Set All PortB to Digital port


' The lookup table has 50 entries long, to get 120° phase shift we need to
' "start" the second phase at 1/3 of the cycle and the third phase at 2/3
' of the table. 50/3=15 so first phase starts at 0, second phase at 15
' and third phase at 30.
' Initilise pointers.

Phase[0] = 0 : Phase[1] = 17 : Phase[2] = 34


High PORTC.3    'Set the initial state for portc.3
Low PORTC.0        'Same
High PORTC.6    'Same
Low PORTC.5        'Same
High PORTB.4    'Same
Low PORTB.3        'Same

Main:

if portb.2=1 then  
  GoSub GetDuty               ' Retrieve the dutycycle values for all three phases
  GoSub SetDutyCycle          ' Set the three PWM modules accordingly


' Now increment the individual table pointers and make sure they wrap
' around to zero when they reach the end of the table. That way they
' will always stay 17 "steps" (120°) from each other.

  
  For i = 0 TO 2
    Phase[i] = Phase[i] + 1
    IF Phase[i] > 50 Then 
    Phase[i] = 0                     'When pointer is > 50 we need to wrap around to 0.
    GoSub ChangeBridgeDrive         'One phase is starting over, go change the outputs.
EndIF
  Next

  PauseUs 77    'Use each duty cycle for 85us before going to another            
  endif
  
if portb.2=0 then
  gosub GetDutyWhenFault
  endif
GoTo Main


SetDutyCycle:
    ' Get value from the array of dutycycles and put it in the dutycycle
    ' registers of the 3 PWM modules. We could have used the array directly
    ' but this way (using a Temp variable) is easier to understand.

    Temp = DutyCycle[0]             ' Get dutycyle for phase 1 from the array and store in temp.
    CCP1CON.4 = Temp.0              ' Set the LSB's 
    CCP1CON.5 = Temp.1 
    CCPR1L    = Temp >> 2           ' Set the 8 high bits

    Temp = DutyCycle[1]             ' Same procedure.
    CCP2CON.4 = Temp.0 
    CCP2CON.5 = Temp.1 
    CCPR2L    = Temp >> 2

    Temp = DutyCycle[2]              ' Same procedure.
    CCP3CON.4 = Temp.0 
    CCP3CON.5 = Temp.1 
    CCPR3L    = Temp >> 2
Return

GetDutyWhenFault:

    Temp = 0             ' Set dutycyle for phase 1 to 0%.
    CCP1CON.4 = Temp.0           ' Set the LSB's 
    CCP1CON.5 = Temp.1 
    CCPR1L    = Temp >> 2         ' Set the 8 high bits

    Temp = 0             ' Same procedure for phase 2
    CCP2CON.4 = Temp.0 
    CCP2CON.5 = Temp.1 
    CCPR2L    = Temp >> 2
    
    
    Temp = 0             ' Same procedure for phase 3
    CCP3CON.4 = Temp.0 
    CCP3CON.5 = Temp.1 
    CCPR3L    = Temp >> 2
return

' -----------------------
'-------------------------------------------------------
' ---- Subroutine to retreive the three dutycycle values from the table.
' ---- Values will be stored in the DutyCycle array.
' ------------------------------------------------------------------------------
GetDuty:
' This For-Next loop runs three times. Each time it gets the value from the lookuptable
' that Phase[i] is pointing at. The Phase array pointers are incremented in the main loop
' and are always 15 "steps" appart so that a 120° phase shift is preserved.

For i = 0 TO 2
  LookUp2 Phase[i], [0,60,130,190,250,310,370,430,480,540,590,640,690,730,770,810,840,870,_
910,930,950,970,980,990,1000,1000,1000,990,980,970,950,930,910,870,840,810,770,730,690,_
640,590,540,480,430,370,310,250,190,130,60,0],Temp


     ' Lookup2 can't handle an array as the designator so we need to 
     ' put the value in a temporary variable first and then move
     ' it to the array of dutycycles.

     DutyCycle[i] = Temp

Next

Return

ChangeBridgeDrive:
 
' When we come here the value i contains the phase counter that just got reset so we
' can use that to determine for which phase we should switch the outputs.
 
Select Case i
    Case 0                          ' It was Phase 1 that rolled over
        Toggle PORTC.3                ' Invert the state of the pin
         Toggle PORTC.0              ' Invert the state of the pin          
                   
 
    Case 1                          ' It was Phase 2 that rolled over
        Toggle PORTC.5              ' Invert the state of the pin
        Toggle PORTC.6              ' Invert the state of the pin
 
 
    Case 2                          ' It was Phase 3 that rolled over
        Toggle PORTB.4              ' Invert the state of the pin
        Toggle PORTB.3              ' Invert the state of the pin
 
 
    End Select
 
Return


End

thanks