Hi srigopal,

There are quite a few ways to do this. Here's one. This version just stops your PWM change.
Code:
Stop_Switch VAR PORTC.0  ' Whatever pin you prefer
Go_Switch   VAR PORTC.1  ' Whatever pin you prefer
Duty        VAR WORD     ' Duty cycle
LowCycle    VAR WORD     ' Low cycle
HighCycle   VAR WORD     ' High cycle
Period      VAR WORD     ' Frequency period
Cycles      VAR WORD     '  
Active      VAR BIT      ' Active/Inactive flag bit
YEP         CON 1        ' PWM will be Active 
NOPE        CON 0        ' PWM will not be Active
End_Cycles  CON 500      ' Increase value to slow PWM duty cycle change

Active = YEP             ' PWM defaults to Active

TRISC = %00000011        ' Make em inputs
TRISB = 0                ' All outs

Period = 500             ' Set frequency here. 500 = ~1.983kHz
                         ' 250 = ~3.825kHz, etc,
Duty = 250               ' Set whatever you prefer here to start with
                         ' 250 = ~50% (1/2 of period)
Main:    
    IF Go_Switch = 0 THEN    ' Go_Switch pressed?
       Active = YEP          ' Yes, toggle flag bit
    ENDIF

    IF Stop_Switch = 0 THEN  ' Stop_Switch pressed?
       Active = NOPE         ' Yes. toggle flag bit
    ENDIF
    
    IF Active = YEP THEN
       IF Duty < Period THEN
          Duty = Duty + 1
       ELSE
          Duty = 0           ' Limit Duty from 0 to 100%
       ENDIF
    ENDIF
    
    ' Compute high & low cycles of Period   
    LowCycle = Period - Duty
    HighCycle = Period - LowCycle
    
    For Cycles = 0 to End_Cycles
        Portb = %00000000 
        Pauseus LowCycle
        Portb = %00000001
        Pauseus HighCycle
    Next Cycles
    
    GOTO Main
And if you want to stop PWM altogether, then a slight change in this routine would do it for you.
Code:
   IF Active = YEP THEN
      For Cycles = 0 to End_Cycles
           Portb = %00000000 
           Pauseus LowCycle
           Portb = %00000001
           Pauseus HighCycle
       Next Cycles
   ENDIF
Of course there are many other ways to do this, but this gives you a good idea of at least 1 way.