Intermittent code cannot run

[Pic2008]

When I first power ON the PIC16F877, sometimes I don't see the LED turn ON, which means my code not running. Anything wrong?

include "modedefs.bas"

define osc 20

asm
 device  pic16f877,hs_osc,BOD_OFF,wdt_off,pwrt_on,protect_off  
endasm

clear
    
    ADCON1=%00000111      'PIC16F877 turn off analog comparator,        
    OPTION_REG.7 = 0     'enable internal pull up GPPU
    OPTION_REG.6 = 0     'falling edge INT
    TRISB = %00010001         
'*********************** ASSEMBLY INTERUPT VARIABLES ***********************
wsave   var     byte $20 system
wsave1  var     byte $a0 system  ' Necessary for devices with RAM in bank1
wsave2  var     byte $120 system ' Necessary for devices with RAM in bank2
wsave3  var     byte $1a0 system ' Necessary for devices with RAM in bank3
ssave   var     byte bank0 system
psave   var     byte bank0 system     

a var byte
b var byte
c var byte
d var byte
task var byte
enc_counter var word
RxD             var PORTC.7
TxD             var PORTC.6
led var PORTE.2

goto start			'skip over interupt handler

'*********************** ASSEMBLY INTERUPT HANDLER *************************

define  INTHAND myint
Asm
       
myint 
  	
	; Save W, STATUS and PCLATH registers, if not done previously
        ;movwf   wsave
        ;swapf   STATUS, W
        ;clrf    STATUS
        ;movwf   ssave
        ;movf    PCLATH, W
       ; movwf   psave  
         
        movlw   high 100      ; Wait 100us to debounce encoder
        movwf   R0 + 1
        movlw   low 500
        call    PAUSEUSL   
       
        incf    _d, w         ;d dummy counter
        nop
        movwf   _d
        
        
        incfsz  _enc_counter,W      ; Add one to low byte
        decf    _enc_counter+1,F    ; No carry (negates next step)
        incf    _enc_counter+1,F    ; Add one to high byte
        movwf   _enc_counter        ; Store updated low byte back.
        iorwf   _enc_counter+1,W    ; Set Z flag
		
	  
	   bsf     _led		    ;turn on led   


        ; Restore saved registers      
        
        movf    psave, W
        movwf   PCLATH
        swapf   ssave, W
        movwf   STATUS
        swapf   wsave, F
        swapf   wsave, W
      
        bcf     INTCON, INTF
        bcf     INTCON, RBIF		  ; Clear the Interupt Flag
        RETFIE                 	  	  ; Return from interrupt
endasm


start:
    intcon=%10011000     ' enable int
    a= 1
   
    high led
    pause 500
    low led

[duncan303]

When I first power ON the PIC16F877, sometimes I don't see the LED turn ON, which means my code not running. Anything wrong?

include "modedefs.bas"

define osc 20

asm
 device  pic16f877,hs_osc,BOD_OFF,wdt_off,pwrt_on,protect_off  
endasm

clear
    
    ADCON1=%00000111      'PIC16F877 turn off analog comparator,        
    OPTION_REG.7 = 0     'enable internal pull up GPPU
    OPTION_REG.6 = 0     'falling edge INT
    TRISB = %00010001         
'*********************** ASSEMBLY INTERUPT VARIABLES ***********************
wsave   var     byte $20 system
wsave1  var     byte $a0 system  ' Necessary for devices with RAM in bank1
wsave2  var     byte $120 system ' Necessary for devices with RAM in bank2
wsave3  var     byte $1a0 system ' Necessary for devices with RAM in bank3
ssave   var     byte bank0 system
psave   var     byte bank0 system     

a var byte
b var byte
c var byte
d var byte
task var byte
enc_counter var word
RxD             var PORTC.7
TxD             var PORTC.6
led var PORTE.2

goto start			'skip over interupt handler

'*********************** ASSEMBLY INTERUPT HANDLER *************************

define  INTHAND myint
Asm
       
myint 
  	
	; Save W, STATUS and PCLATH registers, if not done previously
        ;movwf   wsave
        ;swapf   STATUS, W
        ;clrf    STATUS
        ;movwf   ssave
        ;movf    PCLATH, W
       ; movwf   psave  
         
        movlw   high 100      ; Wait 100us to debounce encoder
        movwf   R0 + 1
        movlw   low 500
        call    PAUSEUSL   
       
        incf    _d, w         ;d dummy counter
        nop
        movwf   _d
        
        
        incfsz  _enc_counter,W      ; Add one to low byte
        decf    _enc_counter+1,F    ; No carry (negates next step)
        incf    _enc_counter+1,F    ; Add one to high byte
        movwf   _enc_counter        ; Store updated low byte back.
        iorwf   _enc_counter+1,W    ; Set Z flag
		
	  
	   bsf     _led		    ;turn on led   


        ; Restore saved registers      
        
        movf    psave, W
        movwf   PCLATH
        swapf   ssave, W
        movwf   STATUS
        swapf   wsave, F
        swapf   wsave, W
      
        bcf     INTCON, INTF
        bcf     INTCON, RBIF		  ; Clear the Interupt Flag
        RETFIE                 	  	  ; Return from interrupt
endasm


start:
    intcon=%10011000     ' enable int
    a= 1
   
    high led
    pause 500
    low led

did you want the led to flash or just come on only once? maybe a goto (somewhere) at the end of the start: routine to create a loop somewhere otherwise the program just ends.

also always good practice to place END at the very end of all programs.

As for the intermittent part try a pause somewhere near the begining of the prog to allow the pic to "settle"

HTH

______

[Pic2008]

Actually I have other code after the LOW led. After many trial and error, if i remove intcon then this problem will not occur.
But this is not the solution because I need the interrupt to enable for it to increment the enc_counter.

[Darrel Taylor]

Calling PBP library routines from ASM interrupt handlers, is generally not a good idea.

The commands will overwrite PBP's system variables in the middle of working on another command in the main program. The effects are completely unpredictable.

In your case, the only system var used by PAUSEUSL is R0. So if you save and restore the R0 Word variable much like psave and ssave, it should work better.
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