Thomas N wrote:

> Hi everyone,
>
> Below is a common LCD display code you often see.  Anyway, I have a small
> problem with it.
>
> When I trace through the code, it goes from line 00082 to line 00085 then
> jump to line 00097 and 00098.  At location 00098, you can see that the
> program counter is 0x0285 (PCL displays 0x85) and W contains value 0.  After
> line 00098 is executed, PCL becomes 0x86.  Next, the program jump to
> location 0x0086 (not 0x0286), which is somewhere else in the code.  WHY?  I
> suspect that the content of PCLATH is overwritten for some reason.  Please
> help!
> Thomas
>
> 027B   3000    00082         MOVLW   0; Table address
> 027C           00083 DISPMSG
> 027C   00AF    00084         MOVWF   TABLE_TEMP  ;start of message
> 027D   2285    00085         CALL    TABLE

O.K. You called TABLE which did a ADDWF to the Program counter,
which pointer the program counter to... TABLE and it tried to execute the
text as code.  I think you want a RETLW for EACH character in the table!


>
> 027E   39FF    00086         ANDLW   0FFH

You don't need to do this when the RETLW is working,
it affects the ZERO bit flag as it fetches the text value.

>

> 027F   1903    00087         BTFSC   STATUS,Z
>
> 0280   2A84    00088         GOTO    OUT
>                00089         call    Send_Char       ; Display character
> 0281   082F    00090         MOVF    TABLE_TEMP,W
> 0282   3E01    00091         ADDLW   1
> 0283   2A7C    00092         GOTO    DISPMSG
> 0284           00093 OUT:
>                00094
> 0284   0008    00095         RETURN
>                00096
> 0285           00097 TABLE:
> 0285   0782    00098         ADDWF   PCL,F           ; Jump to character
> 0286   3454 3468 3469 00099  DT      "This is a test!" ;
>        3473 3420 3469
>        3473 3420 3461
>        3420 3474 3465
>        3473 3474 3421
> 0295           00100 TABLE_END:
> 0295   3400    00101         RETLW   0
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  |  __O    Thomas C. Sefranek   tcs@cmcorp.com
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