Interrupt for a PIC16F877A

triplestak said:

Hey guys,

I have this program in assembly language that I did through MPLABIDE, but my goal is to get the RB0 to be the control Interrupt that makes the count (to 10) output to the LED (PORTA). I have it backwards. The count, automatically starts on the LEDS and when I press RB0 the count is interrupted or "paused" if you will. It continues when I let go. Does anyone have any suggestions to help me reverse this so that RB0 makes the count increment, and when I release it, the count pauses?


hi,
You have a GOTO subr, the subr is ended with a RETFIE, so you get a Stack Underflow error.!
Also the 2nd GOTO.!

Noted that you have a GOTO to the ISR which have named loop.!
goto loop ;Keep on doing this until an interrupt

;***************Interrupt Routine***************

loop: org 0x04 ;interrupt address

movwf TEMP ;temp storage for w
incf COUNT,1 ;Increment COUNT
movlw 0x0A ;Move the value 10 into w
subwf COUNT,0 ;Subtract w from COUNT and result goes to w
btfss STATUS,0 ;Check the Carry flag. Set if COUNT is equal or greater than W
goto continue ;If COUNT is <10, then continue
goto clear ;If COUNT is >9, then clear it

continue: bcf INTCON,1 ;We need to clear this flag to enable interrupts
movfw TEMP ;Restore w to the value before the interrupt
retfie ;Exit the interrupt routine

clear: clrf COUNT ;Set COUNT back to 0
bcf INTCON,1 ;We need to clear this flag to enable interrupts
retfie ;Exit interrupt routine
[/CODE]

Click to expand...

ericgibbs said:

triplestak said:

Hey guys,

I have this program in assembly language that I did through MPLABIDE, but my goal is to get the RB0 to be the control Interrupt that makes the count (to 10) output to the LED (PORTA). I have it backwards. The count, automatically starts on the LEDS and when I press RB0 the count is interrupted or "paused" if you will. It continues when I let go. Does anyone have any suggestions to help me reverse this so that RB0 makes the count increment, and when I release it, the count pauses?


hi,
You have a GOTO subr, the subr is ended with a RETFIE, so you get a Stack Underflow error.!
Also the 2nd GOTO.!

Noted that you have a GOTO to the ISR which have named loop.!
goto loop ;Keep on doing this until an interrupt

;***************Interrupt Routine***************

loop: org 0x04 ;interrupt address

movwf TEMP ;temp storage for w
incf COUNT,1 ;Increment COUNT
movlw 0x0A ;Move the value 10 into w
subwf COUNT,0 ;Subtract w from COUNT and result goes to w
btfss STATUS,0 ;Check the Carry flag. Set if COUNT is equal or greater than W
goto continue ;If COUNT is <10, then continue
goto clear ;If COUNT is >9, then clear it

continue: bcf INTCON,1 ;We need to clear this flag to enable interrupts
movfw TEMP ;Restore w to the value before the interrupt
retfie ;Exit the interrupt routine

clear: clrf COUNT ;Set COUNT back to 0
bcf INTCON,1 ;We need to clear this flag to enable interrupts
retfie ;Exit interrupt routine
[/CODE]

Click to expand...

Eric,

I really appreciate the errors you pointed out. I will be blatantly honest with you. I'm totally new at this. How do I fix the problem exactly? Any help you could give me would be appreciated...

Raj H.

Click to expand...

ericgibbs said:

hi Raj
Look at this edited version of your program, it works OK in simulation.
My advice would be to use the mnemonics names of the SFR [special function registers] rather than bit numbers.
Are you using MPLAB IDE.?

Code:

    processor 16f877a
    include    <p16f877a.inc> 

    errorlevel  -302  , -207 

    __config _RC_OSC & _PWRTE_ON & _WDT_OFF & _CP_OFF &_LVP_OFF

;Set User ID Memory  

;__idlocs        0x1234  


    org    0x00        ;Adress for power up and reset

;*******************SETUP CONSTANTS*******************  

;INTCON    equ    0x0B        ;Interrupt Control Register
;ADCON1    equ    0X9F
;PORTB    equ    0x06
;PORTA    equ    0x05        
;TRISA    equ    0x85       
;TRISB    equ    0x86      
;STATUS    equ    0X03        ;Status register address

COUNT    equ    0x7F        ;This will be our counter variable 
TEMP    equ    0x20        ;Temp file for w register

    org    0x00
    goto    main        ;Jump over the interrupt address

         
;***************Interrupt Routine***************  

isr:    org 0x04        ;interrupt address

    movwf    TEMP        ;temp storage for w 
    incf    COUNT,F        ;Increment COUNT 
    movlw    0x0A        ;Move the value 10 into w
    subwf    COUNT,0        ;Subtract w from COUNT and result goes to w
    btfss    STATUS,0    ;Check the Carry flag. Set if COUNT is equal or greater than W                                        
    goto    continue    ;If COUNT is <10, then continue
    goto    clear        ;If COUNT is >9, then clear it

continue: bcf    INTCON,INTF    ;We need to clear this flag to enable interrupts                                         
    movfw    TEMP        ;Restore w to the value before the interrupt
    retfie            ;Exit the interrupt routine
         
clear:    clrf    COUNT        ;Set COUNT back to 0
    bcf    INTCON,INTF    ;We need to clear this flag to enable interrupts                                            
    retfie            ;Exit interrupt routine
         

;*******************MAIN PROGRAM*********************  

main:
    ;****The Interrupt Registers**** 

    bsf    INTCON,GIE    ;GIE – Global interrupt enable (1=enable)
    bcf    INTCON,INTF    ;INTF - Clear Flag Bit Just In Case
    bsf    INTCON,INTE    ;INTE - RB0 Interrupt Enable (1=enable)
    bsf     INTCON,PEIE

    ;**********Ports***************** 

    bcf    STATUS,RP0
    bcf    STATUS,RP1    ;SET BANK0
    clrf    PORTA
    clrf    PORTB
    bsf    STATUS,RP0    ;Switch to Bank 1
    movlw    b'00000001'        
    movwf    TRISB        ;Set RB0 as input 
    movlw    006h
    movwf    ADCON1
    movlw    b'000000'                        
    movwf    TRISA        ;Set PortA as output
    bcf    STATUS,RP0
    bcf    STATUS,RP1    ; Bank 0
    movf    COUNT,0        ;Move the contents of Count into W
    movwf    PORTA        ;Now move it to Port A


idle_loop:
    nop
    goto    idle_loop        ;Keep on doing this until an interrupt

    end            ;End Of Program

Click to expand...

birdman0_o said:

1) Count isnt initialized before being put in PORTA at the beginning of code

2) No delay ,this will all happen very fast!

3) If you hold down a button using an interrupt on change, it will increase count once!

4) There is no need for an interrupt either ( I usually don't suggest using them for beginners)

5) If you go to CLear, you don't restore context of W (Doesn't matter for this code, but if you made it longer it would matter)

Click to expand...