At 13:46 1998-10-27 -0600, John Payson wrote:
>>Table read has to be made with a jump/call table. (With chips
>>like 16x84 or 12c50x) This is simple when page boundries are
>>not crossed. With non-relocatable code it is simple in that
>>case as well. (Covered well in the Microchip AppNotes)
>
-snip-
>
>I think you could probably do something like:
>
>        ;movwf  TableOffset,w   ; If needed...
>        movlw   HIGH    TableStart
>        movwf   PCLATH
>        movlw   LOW     TableStart      ; Find out the state of the carry
flag
>        addwf   TableOffset,w
>        btfsc   C
>         incf   PCLATH
>        movwf   PCL
>
>Pretty annoying code, though

I can't think of anything more versatile.

But to minimize size and time, we can just let the *compiler* check if the
table crosses a page boundary, and if so warn us.

I use this style:

adtable:
        VARIABLE tablestart = $       ; <-- REMEMBER BEGINNING
        addwf   PCL,F
        retlw   b'00000010'             ; our table...
;etc...
        retlw   b'10010010'
        IF high $ != high adtable     ;<-- COMPARE HIGH BYTE OF START WITH HIG
H BYTE
OF END
                ERROR "addwf PCL overflow in table!"
        ENDIF

So, if we get this error, we either relocate the table, or add Johns code
for run-time method  solution above.

It would have been wonderful if we could have a way to set a variable and
then trigger a second pass for the compiler.  Then we could make some kind
of automated selection of what to  compile, based on earlier compile pass
errors.

(A whish for next MPLAB)

/Morgan
        Morgan Olsson                   ph  +46(0)414 70741
        MORGANS REGLERTEKNIK            fax +46(0)414 70331
        H€LLEK�S    (in A-Z letters: "HALLEKAS")
        SE-277 35 KIVIK, SWEDEN         mrt@iname.com
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