MOV     CX,10              ;load the counter
        SUB     BX,BX              ;clear BX
AGAIN:  MOV     AL,ASC[BX]         ;move to AL content of mem [BX+ASC]
        AND     AL,0FH             ;mask the upper nibble
        MOV     UNPACK[BX],AL      ;move to mem [BX+UNPACK] the AL
        INC     BX                 ;make the pointer to point at next byte
        LOOP    AGAIN              ;loop until it is finished