START           movea.l #0x2300000,a0           ;copy 0x2300000 into a0 (where we read)
            movea.l #0x2310000,a1           ;copy 0x2310000 into a1 (where we write)


LOOP            cmp.l #0x0D, (%a0)          ;exit program if enter key is found
            beq EXIT                ;exit program

            cmp.l #0x30, (%a0)          ;check the range from [30,39]
            blt INVALID_ASCII

            cmp.l #0x39,(%a0)
            bgt GT_39               ;if it's greater than 39

            move.l (%a0),%d0            ;temp variable
            sub.l #0x30,%d0             ;it's within 30-39 range subtract 30 then store result
            move.l %d0,(%a1)            ;copy temp content into result address
            adda #4,%a1             ;increment by 4 bytes
            adda #4,%a0             ;increment by 4 bytes
            clr.l %d0               ;clear content in d0
            bra LOOP                ;branch back to LOOP


GT_39:          cmp.l #0x41, (%a0)          ;if it's less than 41 but greater than 39 then invalid
            ble INVALID_ASCII
            cmp.l #0x46, (%a0)
            bgt GT_46

            move.l (%a0),%d0            ;temp variable
            sub.l #0x31,%d0             ;it's within 41-46 range subtract 31 then store result
            move.l %d0,(%a1)            ;copy temp content into result address
            adda #4,%a1             ;increment by 4 bytes
            adda #4,%a0             ;increment by 4 bytes
            clr.l %d0               ;clear content in d0
            bra LOOP                ;branch back to LOOP



GT_46:          cmp.l #0x61, (%a0)          ;if it's less than 61 but greater than 46 then invalid
            ble INVALID_ASCII
            cmp.l #0x66, (%a0)
            bgt INVALID_ASCII           ;if larger than 66 then it's automatically invalid

            move.l (%a0),%d0            ;temp variable
            sub.l #0x87,%d0             ;it's within 61-66 range subtract 87 then store result
            move.l %d0,(%a1)            ;copy temp content into result address
            adda #4,%a1             ;increment by 4 bytes
            adda #4,%a0             ;increment by 4 bytes
            clr.l %d0               ;clear content in d0
            bra LOOP                ;branch back to LOOP



INVALID_ASCII:      move.l #0xFFFFFFFF, (a1)        ;copy the error code into location of a1
            adda #4,%a1             ;increment address by 4 bytes
            bra loop                ;branch back to the loop


EXIT: