Suppose that your data are written at 10FFh addr of code memory
Use indexed addressing to read the data
in code memory
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org 0000h
MOV A,#0
MOV R0,#0
mov dptr,#10FFh
LOOP103:MOVC A,@A+DPTR
mov r1,a ;before xor
;save data in r1
;very important
;if you don't
;know the value
;in addr 3Fh
xrl a,3fH ; A(XOR)data in 3Fh
jz equal
INC R0
MOV A,R0
CJNE R0,#5,LOOP103
equal: ..............

;look up table
org 10ffh
db 10
db 20
db 30
db 22
db 12
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Vasilis