要求根据寄存器DL中的D3位，完成两个组合BCD数X和Y的加减运算。D3=0，做加法，D3=1，做减法，另外附加了扩张实验-Requirements to complete the combination of the two BCD number of X and Y addition and subtraction in the register DL D3. D3 = 0, addition, D3 = 1, subtraction, in addition to additional e