I am having some issues with what I think to be good code. This is for a uni assignment but this is not the code I'm submitting. This is a test file to understand how it all works. Some of this code was given in the assignment: the snum & binary sections.

I need to get each number in snum in turn and display the equivalent binary number on a 7 segment for a few seconds. It runs in the debugger until 'call binary', then it jumps back to start (after that instructino).

I don't know what I am doing wrong. Any ideas?

; Directive sets processor type .............................

        list  p=16F84A
        #include "P16F84A.INC"

; Set configuration fuses ...................................


; Code protection off, watchdog timer off, power up timer on, RC Clock

        errorlevel  -302        ;No warnings, register not in Bank 0
PCL         EQU     02  ; Program Counter Low
PORTB       EQU     06  ; Port B Data Register
TRISB   EQU 86  ; Port B Data direction register
STATUS  EQU 03  ; Status register
RP0 EQU 05  ; Bank select bit
timer       EQU     0C  ; GPR1 used as delay counter
point       EQU     0D  ; GPR2 used as table pointer

    org 000
    goto    start

snum    addwf   PCL,F
    dt  "0001035020"    ;Substitute your student number
                        ;(10 ASCII digits)

;       Pattern table for seven segment display on Port B ..

binary  addwf   PCL,F
    retlw   b'00111111' ;Set display to 0
    retlw   b'00000110' ;Set display to 1
    retlw   b'01011011' ;Set display to 2
    retlw   b'01001111' ;Set display to 3
    retlw   b'01100110' ;Set display to 4
    retlw   b'01101101' ;Set display to 5
    retlw   b'01111111' ;Set display to 6
    retlw   b'00000111' ;Set display to 7
    retlw   b'01111111' ;Set display to 8
    retlw   b'01101111' ;Set display to 9

; Initialise Port B (Port A defaults to inputs)........

start   bcf STATUS,RP0  ;Bank select 0
    clrf    PORTB   ;Clear Port B data latches
    bsf STATUS,RP0  ;Bank select 1
    movlw   0x00    ;
    movwf   TRISB   ;Set port B lines to output
    bcf STATUS,RP0  ;Bank select 0

nextdigit   movlw   d'10'
    subwf   point,W
    btfsc   3,2
    goto    nextdigit
    movf    point,W
    call    snum
    call    binary
    movwf   PORTB
    incf    point
    goto    nextdigit

  • \$\begingroup\$ Instead of using numbers for registers (btfsc 3,2) I'd recommend you using the register names (btfsc STATUS, Z) for readability. \$\endgroup\$
    – user17592
    Commented May 25, 2013 at 8:24
  • \$\begingroup\$ And use banksel for changing banks, instead of fiddling with the status bits. \$\endgroup\$ Commented May 25, 2013 at 8:51
  • \$\begingroup\$ Have to fiddle part of the assignment learning etc. Thanks for the 3 and 2 thing I have status and Z setup in the larger file but it wasn't working the above was thrown together from many files \$\endgroup\$ Commented May 25, 2013 at 9:04
  • \$\begingroup\$ There is a lot more that could be said about your code, much of which you won't like, but since you've already accepted a answer its pointless anyway. \$\endgroup\$ Commented May 25, 2013 at 15:18

1 Answer 1


You don't initialize the point register. That means it can hold any value when you start looping the nextdigit loop! Try adding a clrf point under the start label.

For debugging: in MPLAB -> View -> File Registers, you can see the value of point during runtime.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.