作者：任治刚
出版社：电子工业出版社
格式: AZW3, DOCX, EPUB, MOBI, PDF, TXT
电子信息工程专业英语教程(第4版)试读：
前言
电子信息工程是国内外飞速发展的工程领域之一。为了应对国际化竞争，大学生必须在学习阶段打下坚实的专业基础，发展全面的职业技能。“熟练运用专业英语、有效进行科技交流”是电子信息工程专业大学生的重要专业素养和必备职业技能。
为了提高学生的专业英语阅读写作能力、拓展学生对电子信息工程关键技术的认识、培养具备国际竞争力的技术人才，《电子信息工程专业英语教程》（Technical English Course for Electronic Information Engineering）充分吸收最新科技成果和英语教学成果，按照先进实用的选材原则和简明系统的组织原则，为电子信息工程专业大学生构建了一个提高英语水平和专业素养的平台。
本教程分为10个主题单元，涵盖了电子信息工程领域的主要技术分支。每个单元由3篇课文、3篇阅读材料和单元练习组成。课文侧重展示基础理论和核心技术；阅读材料着力介绍历史沿革、实用技术和未来前景；单元练习采用完型填空、英汉互译、摘要写作的方式训练语言技能。
本教程各单元包含的具体技术内容如下：
第1～4单元按照“器件”（device）→“电路”（circuit）→“系统”（system）的思路，全景展示了一个典型电子信息系统的构建过程。关于“器件”，我们选择了当今广泛应用的两种ⅤLSI芯片———微处理器和存储器，它们是数字时代电子系统的核心。关于“电路”，我们选择了模拟电路的代表———运算放大器和滤波器，以及混合电路的代表———ADC和DAC，它们是数字时代电子系统的外围。众多功能电路可以构成“系统组件”（component），我们选择了任何电子系统都离不开的“电源设备”（power supply）、“时钟信号源”（clock source）和“互连部件”（interconnect），它们分别相当于系统的“血液”、“心脏”和“筋骨”。关于“系统”，我们选择了移动电话、个人计算机（PC）和全球定位系统（GPS）等。
第5～6单元聚焦两种数字电子系统核心的设计手段。一方面，可以利用ⅤHDL、Ⅴerilog等硬件设计语言，在可编程的FPGA和CPLD芯片上，设计定制的数字电子系统核心。另一方面，可以利用汇编语言、C语言等软件设计语言，在可编程的DSP芯片上，设计功能强大的信号处理核心。在工程实际中，这两种方式往往配合使用。
第7～8单元通过介绍CD、MP3、DSC、HDTⅤ等具体应用，展示了电子信息工程在音频、视频、图像等多媒体领域的发展成果，同时反映出多姿多彩的设计思路和理论成就。学习本单元，有助于激发学生的创新性思维。
第9～10单元面向工程实际，展示了嵌入式产品形成过程的主要方面———选择芯片、选择设计语言、选择操作系统，利用仪器进行测试、验证、故障排除等。关于“芯片”，我们选择了嵌入式领域广泛使用的ARM。关于“语言”，我们介绍了汇编语言、C语言、C++语言、Java语言。关于“操作系统”，我们展示了“实时操作系统”（RTOS）和“嵌入式操作系统”（embedded OS）。关于“仪器测量”，我们选择了3件必备仪器———信号源、示波器、逻辑分析仪，并涉及了“信号完整性”（SI）问题和“虚拟仪器”（ⅤI）应用。
在英语语言技能训练方面，本教程采用了3种方式——完型填空、英汉互译、摘要写作。进行“完型填空”练习，有助于雕琢语言细节——语法、词汇、固定搭配、专业术语、专业表达方法等。进行“英汉互译”练习，有助于明辨英汉语言差异、文化差异和思维方式差异，从而提高专业阅读、学术写作和科技交流的水平。进行“摘要写作”练习，有助于熟悉科技文体格式、用词特点和写作技巧，为将来写作科技论文打下良好基础。
任何语言能力的培养，必须在真实的场景中训练才会收到实效。在本教程中，各单元练习全部取材于国外大学教材、科技专著、国际会议论文、工程技术文档（芯片使用指南、用户手册、技术白皮书）、业内专家文章和著名公司网站等（详见参考文献），以期达到“利用英语学专业、通过专业练英语”的教学目标。
为了便于学生自学，本教程提供了课文参考译文、练习参考答案。此外，本教程在附录中还提供了“科技英语语音手册”和“科技英语词汇手册”。
为了便于教师授课及丰富课堂内容，本教程配有PowerPoint电子讲稿、阅读材料参考译文、视频材料等教辅资料。凡使用本教程作为教材的教师，均可登录电子工业出版社华信教育资源网（www.hxedu.com.cn）注册下载，或者电话联系010-88254531免费获得。
为方便读者查阅，阅读材料参考译文同时以二维码的形式附在相应文后，扫描即可阅读，译文目录：目录
，视频材料：1-1 神秘的磁力1-2 生命的奇迹
本教程自2004年7月出版第1版以来，受到了高校师生和工程技术人员的普遍认可和欢迎。这次修订是在前3版的基础上，充分吸取了每位读者的合理化建议，全面更新了技术内容和语言内容，并增加了附录内容。希望最新版教程更加贴近教学、科研和工程实际。
由于水平所限，书中难免有纰漏和欠妥之处。本教程的读者反馈邮箱为teceie4e＠gmail.com，欢迎各位读者不吝赐教！
编者使用说明
为了提高教授、学习专业英语的效率，这里给出使用《电子信息工程专业英语教程》进行教学和自修的建议。
学生自学建议
正式学习前，建议通读附录。对于没有系统学习过科技英语课程的学生，最好在学习本教程之前，将附录中的“科技英语语音手册”和“科技英语词汇手册”通读一遍。
全面理解核心学术词汇，准确记忆关键科技术语。面对海量英语词汇，必须要有选择。那些出现频率高、词义繁多、用法灵活的词汇是突破的重点。在专业英语学习中，有两类重点词汇——“核心学术词汇”（Core Academic Words）和“关键科技术语”（Key Technical Terms）。请分别参照课文词汇表的New Words&Expressions部分和Technical Terms部分。
泛读课文内容，聚焦英文表达技巧。在对照参考译文阅读课文的时候，不要仅限于明白大概意思就行了，要把主要精力集中于“这个中文意思，英文是怎么表达的?”在很多情况下，英文中有若干种表达方法。那么，通过做笔记、摘抄和总结的办法，就可以不断地积累各种常用的英文表达技巧。
翻译阅读材料，训练技术信息提取能力。作为将来的工程师，显然要具备从英文技术资料中提取关键信息的能力。本教程中的阅读材料包含了丰富的技术题材。如果对于某方面内容特别感兴趣，如GPS系统、软件无线电或HDTV，那么就可以尝试着翻译一下。这也是深入学习词汇、语法和文化的最好方式。
利用单元练习，进行自我测试。本教程中的单元练习，全部来自真实的技术资料，有利于学生测试自己真实的专业英语水平。
教师授课建议
根据教学实际情况，恰当选择精讲课文及段落。本教程的课文难度分为高、中、低三档，适用于各类型大学、各种水平学生的专业英语教学。课文的选材，既有高难度的科技专著、学术会议论文、技术手册，也有中等难度的大学教材、用户手册、技术白皮书，还有比较易懂的综述文章、科普读物。根据实际情况，教师要选择适合课堂教学的内容，作为精讲课文和精讲段落。其他课文和段落，可以安排学生课前预习或课后自学，也可以根本不去涉及。
利用英语学专业，通过专业练英语。专业英语课程实践性很强。在课堂上，教师不但要精讲，更要精练。一段精讲课文，既可以训练学生从中快速、准确提取技术信息的阅读能力，也可以训练学生撰写摘要、模仿造句、独立作文的能力。这种“阅读”→“分析”→“写作”的教学模式，被证明是非常成功的。
适时适量引入音频、视频，丰富课堂内容，激发学习兴趣。为了提高专业英语听说能力，可以在课堂教学中，引入一定量的音视频材料，并设法引导学生学会利用网络进行专业英语的听说读写交流。
强调科技英语阅读写作，提高科技交流职业技能。作为将来的工程师，阅读能力和写作能力最为重要。在科技交流中，无论查询资料、进行设计，还是联系业务，都离不开阅读和写作。有效的科技交流，要求“准确”、“快速”，而这种能力不经过专业训练是无法达到的。尽管出现了自动翻译软件，但实践表明：对于科技翻译，个人的语言素质依然是主导。而专业英语课程承担着训练学生科技交流职业技能的任务。
扩展阅读建议
建议参照下列“大学科技英语”教材，进一步提高、扩展运用专业英语的各方面技能。
科技交流
［1］William Sanborn Pfeiffer，Kaye E.Adkins.大学科技英语国际交流教程.任治刚，译.电子工业出版社，2014.
［2］Charles W.Knisely，Karin I.Knisely.Engineering Communication.Cengage Learning，2014.
［3］Michael Alle.The Craft of Scientific Presentations：Critical Steps to Succeed and Critical Errors to Avoid（2nd Edition）.Springer，2013.
论文写作
［1］John M.Swales，Christine Feak.Academic Writing for Graduate Students（3rd Edition）.ELT，2012.
［2］Robert A.Day，Barbara Gastel.How to Write and Publish a Scientific Paper（7th Edition）.Greenwood，2011.
词汇语法
［1］Alison Pohl，Nick Brieger.Technical English：Vocabulary and Grammar.Summertown Publishing，2002.
［2］Robert A.Day，Nancy Sakaduski.Scientific English：A Guide for Scientists and Other Professionals（3rd Edition）.Greenwood，2011.
［3］Nigel A.Caplan.Grammar Choices for Graduate and Professional Writers.University of Michigan Press/ELT，2012.Unit 1 Electronic DevicesLesson 1 VLSI Technology
One of the key inventions in the history of electronics，and in fact one of the most important inventions over period，was the transistor.It ［1］was invented by Bell Laboratories in 1948.In short，a transistor is a device that conducts a variable amount of electricity through it，depending on how much electricity is input to it.In other words，it is a ［2］digital switch.However，unlike the vacuum tube，it is solid state.This means that it doesn't change its physical form as it switches.There are no moving parts in a transistor.
The advantages of the transistor over the vacuum tube were enormous.Compared to the old technology，transistors were much smaller，faster，and cheaper to manufacture.They were also far more reliable and used much less power.The transistor is what started the ［3］evolution of the modern computer industry in motion.
The transistor was originally a single，discrete device，which you could place individually into a circuit much like any other.Today，some special-purpose transistors are still used that way.What allowed the creation of modern processors was the invention of the integrated circuit，which is a group of transistors manufactured from a single piece of material and connected together internally，without extra ［4］wiring.Integrated circuits are also called ICs or chips.
A special material is used to make these integrated circuits.While most materials either insulate from electrical flow（air，glass，wood）or conduct electricity readily（metals，water），there are some that only conduct electricity a small amount，or only under certain conditions.These are called semiconductors.The most commonly used semiconductor is of course silicon.
By careful chemical composition and arrangement，it is possible to create a very small transistor directly on a layer of silicon，using various technologies to manipulate the material into the correct form.These transistors are small，fast and reliable，and use relatively little power.The first integrated circuit was invented in 1959 by Texas ［5］Instruments.It contained just six transistors on a single semiconductor surface.
After the invention of the integrated circuit，it took very little time to realize the tremendous benefits of miniaturizing and integrating larger numbers of transistors into the same integrated circuit.More transistors（switches）were required in order to implement more ［6］complicated functions.Miniaturization was the key to integrating together large numbers of transistors while increasing hardware speed and keeping power consumption and space requirements manageable.
Large-scale integration（LSI）came to refer to the creation of integrated circuits that had previously been made from multiple discrete components.These devices typically contained hundreds of transistors.Early computers were made from many of these smaller ICs connected together on circuit boards
As time progressed after the invention of LSI integrated circuits，the technology improved and chips became smaller，faster and cheaper.Building on the success of earlier integration efforts，engineers learned to pack more and more logic into a single circuit.This effort became known as very large-scale integration（VLSI）.VLSI circuits can contain millions of transistors.Figure 1.1 The firstmicroprocessor-Intel 4004
Originally，the functions performed by a processor were ［7］implemented using several different logic chips.Intel was the first company to incorporate all of these logic components into a single chip.This was the first microprocessor，the 4004（Figure 1.1），introduced by Intel in 1971.All of today's processors are（highly advanced！）descendants of this original 4-bit CPU.New Words&Expressions
device[dɪˈvaɪs]n.器件 manipulate[məˈnɪpjʊleɪt]vt.处理
conduct[kənˈdʌkt]vt.传导 implement[ˈɪmplɪmənt]vt.实现
inmotion处于活跃状态 consumption[kənˈsʌmp∫ən]n.消耗
discrete[dɪsˈkri：t]adj.离散的 manageable[ˈmænɪdʒəbəl]adj.可处理的
integrated[ˈɪntɪgreɪtɪd]adj.集成的 component[kəmˈpəʊnənt]n.组件
insulate[ˈɪnsjʊleɪt]vt.绝缘 incorporate[ɪnˈkɔ：pəreɪt]vt.合并
silicon[ˈsɪlɪkən]n.硅 descendant[dɪˈsendənt]n.后代Technical Terms
transistor［trænˌsIstə］n.晶体管
semiconductor［ˌsemIkənˌdʌktə］n.半导体
miniaturization［ˌmInIətʃəˌraIˌzeIʃən］n.缩微化
solid state 固态（电路）
LSI abbr.Large-scale Integration 大规模集成（电路）
VLSI abbr.Very Large-scale Integration 超大规模集成（电路）Notes
1.Bell Laboratories是美国的贝尔实验室。
2.“真空管”（vacuum tube）是一种内部气体全部或部分抽空的电子管。
3.此句采用what引导的从句做表语，对主语“the transistor”进行强调。其意思相当于：The transistor started the evolution of the modern computer industry in motion.在这里，“start”为及物动词。
4.此句采用what引导的从句做主语，对表语“the invention of the integrated circuit”进行强调。
5.Texas Instruments是美国的德州仪器公司。
6.“缩微化”（miniaturization）是指减少元件和电路的几何尺寸，从而增加封装密度、降低功耗、减少信号传播延迟。
7.Intel是美国的英特尔公司。1968年，Robert Noyce和Gordon Moore创建了英特尔公司。Lesson 2 Memory Devices
Memories can be made in mechanical，magnetic，optical，biological and electronic technologies.Examples of magnetic memories ［1］are tapes，floppy disks，hard drives and ferroelectric RAMs.Examples of optical memories are CD-ROMs，rewrittable CDs.Electronic memory is used extensively in computer equipment since it is the fastest available.For applications where speed is less important，magnetic and optical technologies are often used.
All electronic memory today can be in separate IC format，module format，or can be part of an IC as a macro-function or cell.In the table below is an overview of some electronic memory（see Table 2.1）.Table 2.1 Overview of Common Electronic Memory Devices
Flip-flop
A flip-flop is basically a bi-state circuit in which either a 0 or 1 state can resides.Because of its simplicity，the flip-flop is extremely fast.As a basic element，the flip-flop is used in digital circuits and ICs.A flip-flop will lose its state when the supply voltage is removed.Therefore，it is volatile.
Register
A register is a set of flip-flops in parallel.Typically a register is 8，16，32 or 64 bits wide.Often a register is used to hold data，address pointers，etc.A register is volatile and very fast just like the flip-flop.
SRAM（Static Random Access Memory）
An SRAM is an array of addressable flip-flops.The array can be configured as such that the data comes out in single bit，4-bit，8-bit，and etc.format.SRAM is simple，fast and volatile just like the flip-flop，its basic memory cell.SRAM can be found on microcontroller boards（either on or off the CPU chip），where the amount of memory required is small and it will not pay off to build the extra interface circuitry for DRAMs.In addition，SRAM is often used as ［2］cache because of its high speed.
SRAM comes in many speed classes，ranging from several ns for cache applications to 200ns for low power applications.SRAM ［3］exists in both bipolar and MOS technology.CMOS technology boasts the highest density and the lowest power consumption.Fast cache memory can be constructed in BiCMOS technology，a hybrid technology that uses bipolar transistors for extra drive.The fastest SRAM memories are available in ECL（Emitter Coupled Logic）bipolar technology.Because of the high power consumption，the memory size is limited in this technology.
A special case of SRAM memory is Content Addressable ［4］Memory（CAM）.In this technology，the memory consists of an array of flip-flops，in which each row is connected to a data comparator.The memory is addressed by presenting data to it（not an address！）.All comparators will then check simultaneously if their corresponding RAM register holds the same data.The CAM will respond with the address of the row（register）corresponding to the original data.The main application for this technology is fast lookup tables.These are often used in network routers.
DRAM（Dynamic Random Access Memory）
The word‘dynamic’indicates that the data is not held in a flip-flop but rather in a storage cell.The data in a storage cell must be refreshed（read out and re-written）regularly because of leakage.The refresh time interval is usually 4 to 64 ms.The storage cell only ［5］requires one capacitor and one transistor，whereas a flip-flop connected in an array requires 6 transistors.In trench capacitor memory technology，which is used in all modern DRAMs，the transistor is constructed above the capacitor so that the space on chip is ultimately minimized.For this reason，DRAM technology has a lower cost per bit than SRAM technology.The disadvantage of the extra circuitry required for refreshing is easily offset by the lower price per bit when using large memory sizes.
DRAM memory is，just like SRAM memory constructed as an array of memory cells.A major difference between SRAM and DRAM，however，lies in the addressing technique.With an SRAM，an address needs to be presented and the chip will respond with presenting the data of the memory cell at the output，or accepting the data at the input and write it into the addressed cell.With DRAM technology，this simple approach is impossible since addressing a row of data without rewriting it will destruct all data in the row because of the dynamic nature.
ROM（Read Only Memory）［6］
ROMs are also called mask -ROMs or mask programmed ROMs.This is because a ROM needs to be programmed by setting its cells to either 0 or 1 at the time of manufacture.Usually the 0 or 1 is formed by the presence or absence of an aluminum line.This aluminum pattern is defined by a lithographic mask used in one of the last steps of manufacture.Therefore these devices are often called mask-ROMs.
The advantage of ROM is that it can be manufactured at the lowest price in high volumes.Another advantage in some applications is that it is impossible to alter the data once the chips are made，and that no further programming and testing are required.On the other hand，if the data or code must be changed this can be a small disaster.The rest of the chips will end in the dustbin and new chips will have to be made.
EEPROM（Electrically Erasable Programmable ROM）
Thismeansthatthechipcan beprogrammedlikean EPROM，butcan beerased electrically.Asaresult，no UⅤsourceisrequired.EEPROMscanbeerasedonabyte-by-bytebasis.New Words&Expressions
mechanical[mɪˈkænɪkəl]adj.机械的 hybrid[ˈhaɪbrɪd]adj.混合的
optical[ˈɒptɪkəl]adj.光学的 simultaneously[saɪməlˈteɪnɪəsli]adv.同时地
format[ˈfɔ：mæt]n.格式 corresponding[ˈkɒrɪˈspɒndɪŋ]adj.相应的
inparallel并行的 dynamic[daɪˈnæmɪk]adj.动态的
static[ˈstætɪk]adj.静态的 whereas[weəˈæz]conj.然而
configure[kənˈfɪgə]vt.配置 approach[əˈprəʊt∫]n.方法
payoff带来利益 pattern[ˈpætən]n.图案
boast[bəʊst]vt.拥有 alter[ˈɔ：ltə]vt.改变Technical Terms
memory［ˌmeməri］n.存储器，内存
magnetic［mæɡˌnetIk］adj.有磁性的
ferroelectric［ˌferəIˌlektrIk］adj.铁电的
volatile［ˌvlətaIl］adj.易失的
register［ˌredʒIstə］n.寄存器
array［əˌreI］n.阵列
cache［kæʃ］n.高速缓存
bipolar［baIˌpələ］adj.双极性的
drive［draIv］n.驱动器
comparator［kəmˌpærətə］n.比较器
leakage［ˌli：kIdʒ］n.泄漏
refresh［rIˌfreʃ］v.刷新
capacitor［kəˌpæsItə］n.电容器
erasable［IˌreIzəbl］adj.可擦除的
programmable［ˌprəɡræməbl］adj.可编程的
lithographic［ˌlIθəˌɡræfIk］adj.平版印刷的
mask［mɑ：sk］n.掩模；掩码；掩蔽
aluminium［ˌælju：ˌmInjəm］n.铝
floppy disk 软盘
macrofunction 宏功能
flip flop 触发器
address pointer 地址指针
interface circuitry 接口电路
trench capacitor 沟道式电容器
ns abbr.nanosecond 纳秒
MOS abbr.Metal-Oxide Semiconductor 金属氧化物半导体
CMOS abbr.Complementary Metal-Oxide Semiconductor 互补金属氧化物半导体
ECL abbr.Emitter Coupled Logic 射极耦合逻辑
UV abbr.ultraviolet 紫外线Notes
1.“铁电”（ferroelectric）是某些材料表现出的一种现象。当在这种材料上施加超过特定强度的电场时，该材料就在一个方向上极化或改变原来的极化方向。只要不受干扰，这种材料就一直保持其极化状态。
2.“高速缓存”（cache）用于存储“频繁使用的”或者“近期使用的”数据，从而提高数据存取速度。高速缓存分为两类：（1）位于处理器内部的“内部缓存”或“存储器缓存”；（2）位于主板上的“外部缓存”或“磁盘缓存”。
3.CMOS是一类集成电路的总称。这种集成电路的输出结构由一个n型 MOSFET（金属—氧化物—半导体场效应晶体管）和一个p型 MOSFET串联而成。因为n型和p型MOSFET是相互补偿的，所以也常常使用“互补”（compementary）一词来说明这种集成电路。
4.CAM是“内容寻址存储器”。它用于实现高速“查找表”（look-up table），但其容量要明显小于DRAM或SRAM。
5.whereas是一个非常正式的词。作为连词，whereas通常表示“但是”、“同时”、“鉴于”。在本句中，whereas表示转折。
6.“掩模”（mask）用于芯片制造过程中。当用紫外线照射时，掩模就会在微处理器的每一层形成不同的电路图案。Lesson 3 Microprocessors
A microprocessor is a complete computation engine that is fabricated on a single chip.The first microprocessor was the Intel 4004，introduced in 1971.The 4004 was not very powerful-all it could do was add and subtract，and it could only do that 4 bits at a time.But it was amazing that everything was on one chip.Prior to the 4004，engineers built computers either from collections of chips or from discrete components.The 4004 powered one of the first portable electronic calculators.
The first microprocessor to make it into a home computer was the Intel 8080，a complete 8-bit computer on one chip，introduced in 1974.The first microprocessor to make a real splash in the market was the Intel 8088，introduced in 1979 and incorporated into the IBM PC.The PC market moved from the 8088 to the 80286 to the 80386 to the 80486 to the Pentium to the Pentium II to the Pentium III to the Pentium 4.All of these microprocessors are made by Intel and all of them are improvements on the basic design of the 8088.The Pentium 4 can execute any piece of code that ran on the original 8088，but it does it about 5，000 times faster！
Table 3.1 shows the differences between the different processors that Intel has introduced over the years.Table 3.1 Intel x86 microprocessors
From this table you can see that，in general，there is a relationship between clock speed and MIPS.The maximum clock speed is a function of the manufacturing process and delays within the chip.There is also a relationship between the number of transistors and MIPS.For example，the 8088 clocked at 5 MHz but only executed at 0.33 MIPS（about one instruction per 15 clock cycles）.Modern processors can often execute at a rate of two instructions per clock cycle.That improvement is directly related to the number of transistors on the chip.
Inside a Microprocessor
A microprocessor executes a collection of machine instructions that tell the processor what to do.Based on the instructions，a microprocessor does three basic things：
● Using its ALU（Arithmetic/Logic Unit），a microprocessor can perform mathematical operations like addition，subtraction，multiplication and division.Modern microprocessors contain complete floating point processors that can perform extremely sophisticated operations on large floating point numbers.
● A microprocessor can move data from one memory location to another.
● A microprocessor can make decisions and jump to a new set of instructions based on those decisions.
There may be very sophisticated things that a microprocessor does，but those are its three basic activities.Figure 3.1 shows an extremely simple microprocessor capable of doing those three things：Figure 3.1 A simple microprocessor
This microprocessor has an address bus that sends an address to memory，a data bus that can send data to memory or receive data from memory，an RD（read）and WR（write）line to tell the memory whether it wants to set or get the addressed location，a clock ［4］line that lets a clock pulse sequence the processor and a reset line that resets the program counter to zero（or whatever）and restarts execution.And let's assume that both the address and data buses are 8 bits wide here.
Here are the components of this simple microprocessor（see Figure 3.1）：
● Registers A，B and C are simply latches made out of flip-flops.
● The address latch is just like registers A，B and C.
● The program counter is a latch with the extra ability to increment by 1 when told to do so，and also to reset to zero when told to do so.
● The ALU could be as simple as an 8-bit adder，or it might be able to add，subtract，multiply and divide 8-bit values.Let's assume the latter here.
● The test register is a special latch that can hold values from comparisons performed in the ALU.An ALU can normally compare two numbers and determine if they are equal，if one is greater than the other，etc.The test register can also normally hold a carry bit from the last stage of the adder.It stores these values in flip-flops and then the instruction decoder can use the values to make decisions.
● There are six boxes marked“3-State”in the diagram.These are ［5］tri-state buffers.A tri-state buffer can pass a 1，a 0 or it can essentially disconnect its output.A tri-state buffer allows multiple outputs to connect to a wire，but only one of them to actually drive a 1 or a 0 onto the line.
试读结束[说明：试读内容隐藏了图片]