传送数据等等。虽然图2-1所示的控制总线看起来是双向的,但它实际上(主要)是单向(大多数都是)信号的集合。大多数信号是从CPU输出到存储器与I/O子系统的,只有少数是从这些子系统输出到CPU的。在介绍指令周期和子系统接口时,我们将详细地讨论这些信号。
A system may have a hierarchy of buses. For example, it may use its address, data, and control buses to access memory, and an I/O controller. The I/O controller, in turn, may access all I/O devices using a second bus, often called an I/O bus or a local bus.
一个系统可能具有分层次的总线。例如,它可能使用地址、数据和控制总线来访问存储器和I/O控制器。I/O控制器可能依次使用第二级总线来访问所有的I/O设备,第二级总线通常称为I/O总线或者局部总线。
The instruction cycle is the procedure a microprocessor goes through to process an instruction. First the microprocessor fetches, or reads, the instruction from memory. Then it decodes the instruction, determining which instruction it has fetched. Finally, it performs the operations necessary to execute the instruction. (Some people also include an additional element in the instruction cycle to store results. Here, we include that operation as part of the execute function.) Each of these functions--fetch, decode, and execute--consists of a sequence of one or more operations.
指令周期是微处理器完成一条指令处理的步骤。首先,微处理器从存储器读取指令,然后将指令译码,辩明它取的是哪一条指令。最后,它完成必要的操作来执行指令(有人认为在指令周期中还要包括一个附加的步骤来存储结果,这里我们把该操作当作执行功能的一部分)。每一个功能??读取、译码和执行都包括一个或多个操作。
Let's start where the computer starts, with the microprocessor fetching the instruction from memory. First, the microprocessor places the address of the instruction on to the address bus. The memory subsystem inputs this address and decodes it to access the sired memory location. (We look at how this decoding occurs when we examine the memory subsystem in more detail later in this chapter.)
我们从微处理器从存储器中取指令开始讲述。首先,微处理器把指令的地址放到地址总线上,然后,存储器子系统从总线上输入该地址并予以译码,去访问指定的存储单元。(译码是如何进行的,我们将在后面的章节中介绍存储器子系统是更为详细的讨论。)
After the microprocessor allows sufficient time for memory to decode the address and access the requested memory location, the microprocessor asserts a READ control signal. The READ signal is a signal on the control bus which the microprocessor asserts when it is ready to read data from memory or an I/O device. (Some processors have a different name for this signal, but all microprocessors have a signal to perform this function.) Depending on the microprocessor, the READ signal may be active high (asserted -
  1) or active low (asserted -
  0).
当微处理器为存储器留出充足的时间来对地址译码和访问所需的存储单元之后,微处理器发出一个读(READ)控制信号。当微处理器准备好可以从存储器或是I/O设备读数据时,它就在控制总线上发一个读信号。(一些处理器对于这个信号有不同的名字,但所有处理器都有这样的信号来执行这个功能。)根据微处理器的不同,读信号可能是高电平有效(信号=
  1),也可能是低电平有效(信号=
  0)。
When the READ signal is asserted, the memory subsystem places the instruction code to be fetched onto the computer system's data bus, The microprocessor then inputs this data from the bus and stores it in one of its internal registers. At this point, the microprocessor has fetched the instruction.
读信号发出后,存储器子系统就把要取的指令码放到计算机的数据总线上,微处理器就从数据总线上输入该数据并且将它存储在其内部的某个寄存器中。至此,微处理器已经取得了指令。
Next, the microprocessor decodes the instruction. Each instruction may require a different sequence of operations to execute the instruction. When the microprocessor decodes the instruction, it determines which instruction it is in order to select the correct sequence of operations to perform. This is done entirely within the microprocessor; it does not use the system buses.
接下来,微处理器对这条指令译码。每一条指令可能要有不同的操作序列来执行。当微处理器对该指令译码是,它确定处理的是哪一条指令以便选择正确的操作序列去执行。这一步完全在微处理器内完成,不需要使用系统总线。
Finally, the microprocessor executes the instruction. The sequence of operations to execute the instruction varies from instruction to instruction. The execute routine may read data from memory, write data to memory, read data from or write data to an I/O device, perform only operations within the CPU, or perform some combination of these operations. We now look at how the computer performs these operations from a system perspective.
最后,微处理器执行该指令。指令不同,执行的操作序列也不同。执行过程可以是从存储器读取数据,写数据到存储器,读或写数据到I/O设备,执行CPU内部操作或者执行多个上述操作的组合。下面我们从系统的角度来看计算机是怎样执行这些操作的。
To read data from memory, the microprocessor performs the same sequence of operations it uses to fetch an instruction from memory. After all, fetching an instruction is simply reading it from memory. Figure 2-2(a) shows the timing of the operations to read data from memory.
微处理器从存储器读取数据所执行的操作序列,同从存储器中去一条指令是一样的。毕竟取指令就是简单地从存储器中读取它。图2-2(a)显示了从存储器中读取数据的操作时序。

  2.
  1.2 Instruction Cycle
In Figure 2-2, notice the top symbol, CLK. This is the computer system clock; the microprocessor uses the system clock to synchronize its operations. The microprocessor places the address onto the bus at the beginning of a clock cycle, a 0/1 sequence of the system clock. One clock cycle later, to allow time for memory to decode the address and access its data, the microprocessor asserts the READ Signal. This causes memory to place its data onto the system data bus. During this clock cycle, the microprocessor reads the data off the system bus and stores it in one of its registers. At the end of the clock cycle it removes the address from the address bus and deasserts the READ signal. Memory then removes the data from the data bus, completing the memory read operation.
在图2-2中,注意最上面的符号CLK,它是计算机的系统时钟,微处理器用系统时钟使其操作同步。在一个时钟周期(系统时钟的0/1序列)的开始位置,微处理器将地址放到总线上。一个时钟周期(允许存储器对地址译码和访问数据的时间)之后,微处理器才发出读信号。这使得存储器将数据放到数据总线上。在这个时钟周期之内,微处理器从系统总线上读取数据,并存储到它的某个寄存器中。在这个时钟周期结束时,微处理器撤消地址总线上的地址,并撤消读信号。然后存储器从数据总线上撤消数据,也就完成了存储器的读操作。
The timing of the memory write operation is shown in Figure 2-2(b). The processor places the address and data onto the system buses during the first clock cycle. The microprocessor then asserts a WRITE control signal (or its equivalent) at the start of the second clock cycle. Just as the READ signal causes memory to read data, the WRITE signal triggers memory to store data. Some time during this cycle, memory writes the data on the data bus to the memory location whose address is on the address bus. At the end of this cycle, the processor completes the memory write operation by removing the address and data from the system buses and deasserting the WRITE signal.
存储器写操作的时序如图2-2(b)所示。在第一个时钟周期,处理器将地址和数据放到总线上,然后在第二个时钟周期开始 时发出一个写(WRITE)控制信号(或与之等价的信号)。像读信号促使存储器读取数据一样,写信号促使存储器存储数据。在这个时钟周期的某个时刻,存储器将数据总线上的数据写入地址总线指示的存储单元内。当这个时钟周期结束,微处理器从系统总线上撤消地址、数据及写信号后,就完成了存储器的写操作。
The I/O read and write operations are similar to the memory read and write operations. A processor may use either memory mapped I/O or isolated I/O. If the processor supports memory mapped I/O, it follows the same sequences of operations to input or output data as to read data from or write data to memory, the sequences shown in Figure 2-
  2. (Remember, in memory mapped I/O, the processor treats an I/O port as a memory location, so it is reasonable to treat an I/O data access the same as a memory access.) Processors that use isolated I/O follow the same process but have a second control signal to distinguish between I/O and memory accesses. (CPUs that use isolated I/O can have a memory location and an I/O port with the same address, which makes this extra signal necessary.)
I/O的读写操作与存储器的读写操作类似。处理器可以使用存储器影射I/O或者是单独I/O。如果处理器支持存储器影射I/O,则它遵循从存储器读写数据同样的操作顺序,该顺序如图2-2所示(记住,在存储器影射I/O中,处理器把一个I/O端口当作某个存储单元,当然I/O的数据访问同存储器的数据访问一样的)。使用单独I/O的处理器遵循同样的处理过程,但是另有一个控制信号用以区别是I/O访问还是存储器访问(使用单独I/O的CPU允许一个存储单元和某个I/O端口具有相同的地址,因此需要这一额外的信号加以区分)。
Finally, consider instructions that are executed entirely within the microprocessor. The INAC instruction of the Relatively Simple CPU, and the MOV r1, r2 instruction of the 8085 microprocessor, can be executed without accessing memory or I/O devices. As with instruction decoding, the execution of these instructions does not make use of the system buses.
最后,考虑一下完全在微处理器内部执行的指令。相对简单CPU的INAC指令和8085的MOV r
  1,r2指令的执行都不要访问存储器和I/O设备。按照指令译码的结果,这些指令的执行不会用到系统总线。
New Words & Expressions:
latch v.闭锁,锁存program counter 程序计数器
instruction register 指令寄存器operand n. 操作数
increment n.增量,加1flag register 标志寄存器
pipeline n.流水线microsequenced 微层序的
local bus 局部总线
Abbreviations:
ALU (Arithmetic Logic Unit) 算术逻辑单元
The CPU controls the computer. It fetches instructions from memory, supplying the address and control signals needed by memory to access its data. The CPU decodes the instruction and controls the execution procedure. It performs some operations internally, and supplies the address, data, and control signals needed by memory and I/O devices to execute the instruction. Nothing happens in the computer unless the CPU causes it to happen.
CPU控制整个计算机。它从存储器中取指令,提供存储器需要的地址和控制信号。CPU对指令译码并且控制整个执行过程。它执行一些内部操作,并且为存储器和I/O设备执行指令提供必要的地址、数据和控制信号。除非CPU激发,否则,计算机什么事情都不会发生。
Internally, the CPU has three sections, as shown in Figure 2-
  3. The register sections, as its name implies, includes a set of registers and a bus or other communication mechanism. The registers in a processor's instruction set architecture are found in this section of the CPU. The system address and data buses interact with this section of the CPU. The register section also contains other registers that are not directly accessible by the programmer. The relatively simple CPU includes registers to latch the address being accessed in memory and a temporary storage register, as well as other registers that are not a part of its instruction set architecture.
CPU内部有三大分区,如图2-3所示。寄存器区,顾名思义,它包括一组寄存器、一条总线或其他通信机制。微处理器指令集结构中的寄存器就属于CPU的这一分区。系统的地址和数据总线与寄存器交互。此分区还包括程序员不能直接访问的一些寄存器。相对简单CPU含有寄存器用以锁存正在访问的存储器地址,还有暂存器以及指令集结构中没有的其他寄存器等。
During the fetch portion of the instruction cycle, the processor first outputs the address of the instruction onto the address bus. The processor has a register called the program
 

相关内容

计算机专业英语教程

   计算机专业英语教程 2010.5.1 Computer science major course Computer English Chapter 1 The History and Future of Computers As a computer science student,we should study English hard This book is very important to us Key points: useful terms a ...

计算机专业英语翻译

   高新电脑学校 ?? 计算机组装与维护 课件制作:孙波 IT CFAC gaoxindiannaoxuexiao 国家计算机教育认证 计算机英语 计算机英语词汇对译 K 千,存储空间的容量单位, kilobyte,1K=1024 字节。 M 兆,megabyte,1M=1024K。 G 吉,gigabyte,1G=1024M。 T 太,1T=1024G。 PC personal computer 个人计算机 IBM International Business Machine 美国国际商用机器 ...

计算机专业英语

   《计算机专业英语词汇》 编辑本段 A Active-matrix 主动矩阵 Adapter cards 适配卡 Advanced application 高级应用 Analytical graph 分析图表 Analyze 分析 Animations 动画 Application software 应用软件 Arithmetic operations 算术运算 Audio-output device 音频输出设备 Access time 存取时间 access 存取 accuracy 准确性 ...

计算机专业英语

   中等职业教育“十一五”规划教 材 计算机专业英语 杨利 方风波 科学出版社 主编 目录 第1章 第2章 第3章 第4章 第5章 第6章 第7章 第8章 计算机专业英语简介 计算机专业英语的词汇学习 屏幕英语 计算机说明书 计算机专业论文 网络英语 计算机专业英语试题汇编 阅读材料 第1章 计算机专业英语简介 1.1 计算机专业英语与普通英语的异同 " 1.1.1为什么要学习计算机专业英语 1.1.1为什么要学习计算机专业英语 " 1.1.2计算机专业英语与普通英语的相同点 1.1.2计算机 ...

计算机专业英语

   中等职业教育“十一五”规划教 材 计算机专业英语 杨利 方风波 科学出版社 主编 目录 第1章 第2章 第3章 第4章 第5章 第6章 第7章 第8章 计算机专业英语简介 计算机专业英语的词汇学习 屏幕英语 计算机说明书 计算机专业论文 网络英语 计算机专业英语试题汇编 阅读材料 第1章 计算机专业英语简介 1.1 计算机专业英语与普通英语的异同 " 1.1.1为什么要学习计算机专业英语 1.1.1为什么要学习计算机专业英语 " 1.1.2计算机专业英语与普通英语的相同点 1.1.2计算机 ...

计算机专业英语

   中等职业教育“十一五”规划教 材 计算机专业英语 杨利 方风波 科学出版社 主编 目录 第1章 第2章 第3章 第4章 第5章 第6章 第7章 第8章 计算机专业英语简介 计算机专业英语的词汇学习 屏幕英语 计算机说明书 计算机专业论文 网络英语 计算机专业英语试题汇编 阅读材料 第1章 计算机专业英语简介 1.1 计算机专业英语与普通英语的异同 " 1.1.1为什么要学习计算机专业英语 1.1.1为什么要学习计算机专业英语 " 1.1.2计算机专业英语与普通英语的相同点 1.1.2计算机 ...

计算机专业英语教程

   21 g g + J &,3 / (21 ISBN 7301095058 1. . CIP . 2005 ü 092463 ü : ü .H31 . ü ) : 2005.8 ISBN 7-301-09505-8/Gg1596 100871 http://www.pup.cn http://www.pup6.com 62752015 pup_6@163.com 62750672 62750667 62754962 62752015 787 2005 20.00 h1092 9 1 1 ...

计算机专业英语教程ppt5

   五、借用词 借用词一般来自厂商名、商标名、产品代号名、发明者名、地名等, 借用词一般来自厂商名、商标名、产品代号名、发明者名、地名等,它 通过将普通公共英语词汇演变成专业词意而实现。 通过将普通公共英语词汇演变成专业词意而实现。有的则是将原来已经 有的词汇赋予新的含义。 有的词汇赋予新的含义。例如: woofer 低音喇叭 tweeter 高音喇叭 flag标志、状态 cache 高速缓存 semaphore 信号量 firewall 防火墙 mailbomb 邮件炸弹 scratch pa ...

计算机专业英语

   A 算盘 抽象数据类型 抽象 抽象工具 Access(微软的数据库系统) 存取时间 (一个进程的)激活 活动服务器界面 角色 Actors 实参 actual parameter access time activation(of a procedure) Active Server Pages,ASP abacus abstract data type abstraction abstract tools Ada(一种基于 pascal 的程序设计语言) 自适应词典编码 适配器模式 (存储 ...

计算机专业英语

   计算机专业英语 Computer English 南京市财经学校校本教材 南京市财经学校校本教材 1 Contents 目录 Part One Computer hardware and software 计算机硬件和软件 计算机硬件和软件 硬件和软件盖金曙 生家峰 盖金曙 Unit 1 the History of Computers 计算机的历史 Unit 2 Computer System 计算机系统 Unit 3 Disks and Disk Drives 磁盘和磁盘驱动器 Unit ...

热门内容

英语易混单词总汇

   英语易混易错词汇总结 1. clothes, cloth, clothing clothes 统指各种衣服,谓语动词永远是复数, cloth 指布,为不可数名词 clothing 服装的 总称,指一件衣服用 a piece of, an article of 2. incident, accident incident 指小事件, accident 指不幸的事故 He was killed in the accident. 3. amount, number amount 后接不可数名词, ...

考研英语语法全突破

   考研俱乐部 --考研英语语法全突破 1 很多英语老师都面临着一大烦恼,特别是农村中学的英语老师们,在农村小学英语基础教育没有走上正轨以 及缺乏多媒体教学条件的情况下,学生不爱听课,要么走神,要么就干别的事,好像对老师所讲的一点儿不 感兴趣。究其原因,是由于课堂教学枯燥乏味。因此,教师的当务之急便是努力增加课堂的趣味性,让英语 课堂不再乏味。该如何增加课堂的趣味性呢?下面是我的几点体会: 一、讲一些文化背景 语言是文化的重要载体,语言与文化密不可分。学习语言只有了解了有关的文化知识后,才能正确 ...

大学英语四级阅读理解精读100篇

   Passage One (Clinton Is Right) President Clinton’s decision on Apr.8 to send Chinese Premier Zhu Rongji packing without an agreement on China’s entry into the World Trade Organization seemed to be a massive miscalculation. The President took a drub ...

文刀川页丛书高考英语短文改错应试技巧点拨

   文刀川页丛书 题型专项 短文改错 !! 用等。 一、考点聚焦 1、题型特点 (1)词法内容。包括名词、代词的数与格,反身代词,动词时态语态,非谓语动词、 短语动词的用法,不规则动词的变化形式,形容词的比较级,形容词副词的区别,介词的误 (2)句法内容。包括主谓一致、指代一致,并列连词,从属连词等引导各种从句的关 联词语,感叹句,疑问句,祈使句的结构等。 (3)行文逻辑。包括句子的肯定、否定、推理、判断等。 二、应试技巧点拨 (1)通读全文,了解文章主旨大意,确定文章的题材、体裁,把握文章的背 ...

英语六级句子

       本文由五分钟的热度贡献     背7个句子,6级作文拿100分 .四级照样百分     6级作文模板:     1)先背3个句子     1 Nowadays with the rapid development of advanced ……., more and mor e….. are commonly and widely used in everyday life.(讲重要性)     2 The popularity of digital …will have great  ...