某计算机的地址线、数据线均为8位，一条两字节的相对寻址的无条件转移指令，存于内存20H和21H单元中，指令操作码存放在20H中，存放在21H中的位移量为15H。则取该指令时PC(程序计数器)为（）H，该指令执行结束时PC为（请作答此空）H。
- A.21
- B.35
- C.37
- D.41
正确答案及解析
正确答案
解析
由于两个字节的相对寻址的无条件转移指令存于内存20H单元和21H单元中，当 CPU准备取出该指令时，PC的内容必定指向存放该指令第一个字节的地址，即PC=20H。当CPU取出该指令准备执行时，PC的内容为22H，而取出的位移量为15H，执行该指令时是：PC+位移量→PC。因此，该指令执行结束时PC为37H。
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