ASCII codes 30 to 39 represent 0 to 9 in binary and 41 to 46 represent A to F. Therefore
if the ASCII code is between 30-39h then 30h is subtracted from the code. If the number
lies between A to F then 37h is subtracted from the code to get its binary equivalent
mov dptr, #9000h ;load dptr with address 9000h
movx a,@dptr ; move data from external memory location to a
clr c ;clear carry bit
mov r1,a ;move data from a to r1
subb a,#40h ;subtract 40h from a
jc l2 ;jump to location l2, if carry
mov a,r1 ;move data from r1 to a
subb a,#37h ;subtract with borrow, 37h from a
sjmp here ;jump to location here
l2:mov a,r1 ;move data from r1 to a
clr c ;clear carry bit
subb a,#30h ;subtract with borrow, 30h from a
here:inc dptr ;increment dptr
movx @dptr,a ;move data from a to external memory location
rep:sjmp rep
end
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