On Thu, 4 Sep 2003 19:06:52 EDT, you wrote:

>Hi all!
>                Had a look at the piclist memory method big lookup tables and
>AN556 implementing table read now I am confused!!
>
>
>
>
>                 I am trying to get data from a large lookup table in Page 1
>of 16f873- (similar table in page0 seems to work fine) This is the first time
>I have used anything larger than a 16f628 so I think I may have messed up with
>Page selecting and clearing.
>
>

You're on the right track and yes, page select is causing the problems
that you're seeing. You need to make this part of your code its own
page 0 subroutine and put just the data in the upper bank. You then
call this subroutine from your mainline code.

I hope the spacing turns out to be readable.

;
;    do a table lookup based on 'overflow' and 'fine' values
;
;    Note: changes PCLATH - must do a pagesel after calling
;
;
GetTable:
    movlw    high(Table1)   ; get upper portion of Table1 base address
    movwf    PCLATH
    movf      overflow, w     ; get which 256-byte portion of Table1
    addwf    PCLATH, f     ; now pointing to right portion of table

    movf      fine, w             ; get offset into 256 byte page
    movwf    PCL                ; branch directly into table

;
;    NOTE: no return needed, executing the retlw in Table1 returns
;     to wherever GetTable was called from
;


From your mainline code, this would be used as:

;
;    set up your overflow and fine variables
;
    call         GetTable        ; convert to table value
    pagesel $+1                 ; restore PCLATH to current page
;
;    use the returned value in W as needed
;

>;;;;;;;;;;;Table:::::::::::::::::::::::
>       org      800h                 ;page1
>
>Table1
>       movf     pcl,f               ;using this seems to rollover at every
>256th value
^^^^^
Remove the above line to start your data at location 0800h

>       retlw     .1
>       retlw     .5
>       retlw     .2
>       retlw     .12
>       retlw      .6


Hope this helps.

Regards, Bob

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