问题描述
请考虑以下微操作顺序.
Consider the following sequence of micro-operations.
MBR ← PC
MAR ← X
PC ← Y
Memory ← MBR
以下哪个是该序列可能执行的操作?
Which one of the following is a possible operation performed by this sequence?
- 指令提取
- 操作数获取
- 条件分支
- 启动中断服务
答案是选项(4).
Answer is option (4).
我的尝试:
- 指令提取:提取指令:从PC中的地址读取指令代码，并将其放置在IR中. (IR←内存[PC])
- 操作数获取:如有必要，从内存中获取操作数:如果任何操作数是内存地址，请启动内存读取周期以将其读入CPU寄存器.如果操作数在内存中而不是寄存器中，则该操作数的内存地址称为有效地址，简称EA.因此，操作数的提取可以表示为寄存器←存储器[EA].在当今的计算机上，CPU比内存快得多，因此操作数提取通常需要多个CPU时钟周期才能完成.
- 如果满足条件(且寄存器不为0)，则条件分支指令将PSW中的位置计数器设置为寄存器或寄存器中指定的地址加上12位偏移量
- 中断服务例程(ISR)是硬件响应中断而调用的软件例程. ISR检查中断并确定如何处理它. ISR处理中断，然后返回逻辑中断值.
推荐答案
此问题使用William Stalling的教科书.该问题本身没有足够的背景材料，供不熟悉Stalling教科书的人回答(我不拥有Stalling的教科书，也不知道此问题引用的版本).
This question uses notation from one of William Stalling's Computer Organization and Architecture textbooks. The question itself does not contain enough background material for someone unfamiliar with Stalling's textbook to answer it (I do not own Stalling's textbook, or know which version this question references).
但是，在另一个网站上看到指向答案的评论后，我在Google搜索了规则"用于时钟周期分组".这导致了一系列指向各种不同幻灯片的链接.
However, after seeing the comment that pointed to an answer at another site, I Googled for "rules for clock cycle grouping". That led to a bunch of links that pointed to various different sets of slides.
对我来说，第三个链接是 PowerPoint演示文稿包括一张我已在下面复制为图片的幻灯片.有一张幻灯片解释了MAR和MBR代表什么:
The third link for me was to a powerpoint presentation which included a slide that I have copied below as an image. There was a slide that explained what MAR and MBR stand for:
-
已连接到地址总线
Connected to address bus
指定用于读取或写入操作的地址
Specifies address for read or write op
内存缓冲寄存器(MBR)
Memory Buffer Register (MBR)
-
已连接到数据总线
Connected to data bus
保留要写入的数据或最后读取的数据
Holds data to write or last data read
因此，似乎正在发生的事情是先将PC放在MBR中.接下来，将保存PC的地址从X复制到MAR.在同一循环中，PC设置为中断服务程序的开始，而该服务在Y中可用.最后，MBR中的数据通过总线传输到内存中.
So it appears that what is happening is that first the PC is placed in MBR. Next the address for where the PC will be saved is copied from X to MAR. In the same cycle the PC is set to the start of the interrupt service routine which is available in Y. Finally the data in MBR is transferred on the bus to memory.
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