Nguyen Duc Toan wrote:
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Well patrick

I wrote this code with Michael's suggestion. I think he's right. And I can't any problem with the 'logic'.

org 0
jmp main
org 30h
main :
...
I put the table just behind subroutine LookUp.
I had simulated this code many time any all results are the same : DPTR=03EB

I think movc A,@A+DPTR will pull data from the address that pointed by DPTR's content.

ACCESS_INDEX equ 864
ACCESS_COUNT equ 864

main:

MOV R6, #HIGH(ACCESS_INDEX) ;R6=03 (hex)
MOV R7, #LOW(ACCESS_INDEX) ;R7=60 (hex)
;
; Subruotine
LOOKUP3:
mov a, #low(table) ; A=8B (hex)
add a, r7 ; A=EB (hex)
mov dpl, a ; DPTR=00EB
mov a, #high(table) ; A=03 

you load A with 03H

addc a, r6 ; A=03

You add contents of R6 (loaded 03H) to A

mov dph, a ; DPTR=03EB

I think 06EBH is in DPTR

clr a ; A=00
movc A, @A+DPTR ; A=00 (hex)??? A(should)= 4B
RET
table:
DB #04Bh 

I can be wrong, but I think yor DPTR does not contain 03EB

regards
Patrick