This "high" keyword is excellent.  Much nicer, I agree.

However, I don't understand why you say "Saving W around setting
PCLATH is pointless because you are about to trash the old W value
with the table entry value."

The value in W is the digit value that needs to be converted
to a 7-segment pattern.  For example...
        ...
        movf    DIGIT0,W
        call    Convert7Seg
        ...

In the code sample you added, that value is thrown out.




-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Olin Lathrop
Sent: Wednesday, June 12, 2002 7:32 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]: Odd problem...


>         org     0x0700          ; Start in really high memory
>         ;-----------------------------------------------------
>         ;   Convert 4-digit data to 7-segment data
>         ;-----------------------------------------------------
>
> Convert7Seg:
>         movwf   SAVE_ADDR       ; Save offset
>         movlw   0x07
>         movwf   PCLATH
>         movf    SAVE_ADDR,W     ; Retrieve offset

Saving W around setting PCLATH is pointless because you are about to trash
the old W value with the table entry value.

I also don't like the MOVLW 7 to get the constant to load into PCLATH.  If
you change the ORG value, you have to remember to change this value.  Worse,
you didn't even document this dependecy.  A far better answer is to have the
assembler load the right value for you automatically.  I've added a label to
the start of the table for that purpose:

          movlw   high table1     ;set the high bits of the table entry adr
          movwf   pclath

>         addwf   PCL,F           ; Jump to appropriate offset
table1                            ;start address of the table
>         retlw   B'01111110'     ; '0'
>         retlw   B'00110000'     ; '1'
>         .
>         .
>         .
>         nop                     ; Error - '15'
>         retlw   B'00000001'     ; Return dash


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