Hi John!

You should take care of 256 bytes page boundaries in PIC16 architecture.
You need to broke your 1k-words table in four 256 bytes tables.
Realy, it is worst: you need to write a small code in
 the beginning of each page
in order to assure that high PC bits are correct.
Or, in a different approach, you need adjust PCLATH
before each table jump.


Another thing: the first table (at bank 0)
may be of less entries
that follower tables.
A example of using tables is like this:

; RAM variables

OFFSETT_0    equ        0x25 ; Variable that holds offsett for Table_0
OTHER           equ     0x26 ; Other variable
OFFSETT_1       equ     0x27 ; Variable that holds offsett for Table_0

OFFSETT_2       equ     0x37 ; Variable that holds offsett for Table_0
ANOTHER EQU    0X39 ; Another :)
OFFSETT_3       equ     0x3A ; Variable that holds offsett for Table_0


        ORG 0x000
        goto    MAIN

        ORG 0x004
INTERRUPT_SERVICE
      ; Put code for interrupt here

MAIN
        ; Put code for initialization here

Main_Loop
        ; Put some code of main loop here

Read_Table_0
        movf    OFFSETT_1, W
        call    Table_0
        ; use value returned in W

Read_Table_1
        movf    OFFSETT_1, W
        call    Table_1
        ; use value returned in W

Read_Table_2
        movf    OFFSETT_2, W
        call    Table_2
        ; use value returned in W

Read_Table_3
        movf    OFFSETT_3, W
        call    Table_3
        ; use value returned in W

        ; Put the last code of the mainline here.
        goto Main_Loop
;
;----- Table's zone can begins here ------------------------
;

        ORG  0x57       ; Say that, for example, the next free
                        ; memory program position is 0x57
Table_0
        clrf    PCLATH  ; Position 0x057 used by table header.
        addwf   PCL, F ; Position 0x058 used by table header.

        retlw   0x21    ; First really util postion: 0x059
        retlw   0x05   ; Second usable position: 0x05A
        ...
        retlw   0x45   ; Last usable position in table 0 is at 0x0FF


        ORG 100
Table_1
        bsf  PCLATH, 0    ; Position 0 of bank 1 at 0x100
        bcf  PCLATH, 1    ; Position 1 of bank 1 at 0x101
        addwf   PCL, F

       retlw    0x45        ; First really usable position: 0x103
        retlw  0x58         ; Second position: 0x104
        ....
       retlw  0x13          ; Last position in this bank: 0x1FF

        ORG 200
Table_2
        bcf     PCLATH, 0 ; Assure that PCLATH is equal to 0x02
        bsf     PCLATH, 1
        addwf   PCL, F

        retlw   0x76    ; First table entry at position 0x203
        retlw   0x23    ; Second at 0x204
         ....
        retlw   0x98    ; Last entry in Table_2 at 0x2FF

        ORG     0x300
Table_3
        bsf     PCLATH, 0
        bsf     PCLATH, 1 ; PCLATH is equal to 0x03
        addwf   PCL, F

        retlw   0x83    ; First in this bank at 0x303
        retlw   0x37
        ...
        retlw   0x36    ; Last position in the whole PIC16F84 is at 0x3FF


Hope this will help...
Cheers! :)

At 20:05 27/11/00 -0800, you wrote:
>Being a closet AVR person, I have come to the point where I must use a pic
>for this application.
>
>I have taken a crash course on the 16F84, and came to the conclusion there
>are no page bounderies on the 1K program memory block. I want to fill the
>whole program memory with a data table using retlw's, and a short program
>to run through the complete data table continuosly. Am I correct about no
>page bounderies? Anything I should be aware of in doing this?
>
>Thanks for any help
>
>John
>
>--
>http://www.piclist.com hint: To leave the PICList
>mailto:piclist-unsubscribe-request@mitvma.mit.edu
>
>
>
>

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