For input interface, perhaps the main problem facing the designer is that of electrical noise .Small noise signal may cause the system to malfunction, while larger amounts of moist can permanently damage it. The designer must be aware of these dangers from the outset. There are many methods to protect interface circuits and microcomputer from various kinds of noise .Following is some examples:
Input and output electrical isolating between the microcomputer system and external devices using an opt-isolator or a transformer.
1.Removing high frequency noise pulses by a low-pea filter and Schmitt-trigger.
1.Protecting against excessive input voltages using a pair of diodes to power supply reversibly biased in normal direction.
对于输入接口，也许设计所面临的主要问题是电噪声，小噪声信号会引起系统工作不良，而大量的噪声会造成永久性的损坏。设计者必须从一开始就清楚这些危险。有许多方法保护接口电路和微机不受各种各样的噪声影响下面是一些例子： 1，使用光电隔离或变压器实现微机系统和外部器件之间的输入输出电信号隔离。 2用一低通滤波器和一施密特触发器排除高频噪声脉冲。3，用一对二级管以反向偏置于正常方向的形式连接至电源端，来保护过高的输入电压
For output interface, parameters VOH, VOL, IOH and IOL of a logic device are usually much to low to allow loads to be connected directly, and in practice an external circuit must be connected to amplify the current and voltage to drive a load. Although several types of semiconductor devices are now available for controlling DC and AC powers up to many kilowatts, there are two basic ways in which a switch can be connected to a load to control it : series connection and shunt connection as shown in Figure 18.3.
对于输出接口，一逻辑器件的参数VOL，VOH, IOL, IOH， 往往太小而不能直接与负载相连，实践中必须在一个外部电路将电流和电压进行放大以驱动一负载。现在尽管有一些类型的半导体器件可用于将DC和AC的功率控制若干千瓦，有两种基本方式将开关连至负载。如图的串联连接和并联连接。
With series connection, the switch allows current to flow through the load when closed, while with shunt connection closing the switch allows current to bypass the load.
Both connections are useful in low-power circuits, but only the series connection can be used in high-power circuits because of the power wasted in the series resistor R.
对于串联连接，开关闭合时使电流流过负载，而当并联连接时和上开关使电流绕过负载。两种方式都可用于低功率电路中，但只有串联连接才能用于高功率电路，这是因为串联电阻R上要消耗功率。
The field of communications is experiencing rapid and dramatic change. Traditionally, telecommunications has been the transmission of information over long distances by means of telephone, teletype, radio, or television. Data communications has been the exchange of data between computer-related devices. Today, these distinctions have blurred as the two have been converging into networks—a group of computers and other devices connected by communication facilities—in which information is processed and communicated in the form of sound, data, and images over common media.
通信技术的领域经历了一个很快的令人瞩目的改变。过去，远程通信通过电话，电报，收音机或者电视。数据通信已经成为了计算机设备之间的数据交换。如今，这个区别已经变得模糊了，因为这两个种类已经被覆盖在网络里 一组计算机和其他设备连接的通信设施，一个息处理和流通的地方通过公共媒体以生意数据和图像的方式。
What does this change mean for society? Just as during the late 1800s and early 1900s global societies were shaped by such technologies as ships, electricity, and the internal combustion engine, so in the late 1900s and early 2000s they will be shaped by converging computer and communication technologies. The increased capabilities of the networks allow providers to offer a wider variety of communication services (e.g., video, facsimile, data, and multimedia services) than the traditional voice services. How we obtain news and entertainment, conduct business and education, and accomplish scientific and technical research will all be affected.[
这个改变对于社会意味着什么？就像18世纪末到19世纪早期的社会是由船，电子产品，内燃机等技术组成的。所以20世纪末，到21世纪初他们将会由计算机和通信技术所融合。网络性能的增长允许供应商提供更多样化的通信服务（例如，视频，数据，传真，和多媒体服务）比传统的语音服务。我们如何获得新闻和娱乐，进行商业和教育，实现科学和技术研究都将受到影响。
Networks can be analog, in which information is represented by continuous smoothly varying signals, or digital, in which information is represented by discrete on/off signals.[2]
Digital signals are a newer technology found in computer systems, local area networks, compact disks, and high definition television(HDTV). Digital signals are discrete on/off signals that can be easily stored, compressed, edited, and manipulated. The telephone industry is in the process of converting to an all digital network called Integrated Services Digital Network(ISDN) and similar upgrades are proposed for cellular telephone networks. 网络可以是模拟量，其中的信息是由连续平稳变化的信号，或数字，其中的信息是由离散的开/关信号描绘的。数字信号是一个较新的技术，在计算机系统，局域网，光盘，和高清晰度电视中应用。数字信号是离散的开/关信号，可以很容易地压缩，存储，编辑，和操纵。电话产业是一个改变被称为信号数据的完全数字网络的发生，类似的升级也被提议用在蜂窝式电路网络。
There are three major categories of networks distinguished primarily by geography: wide-area networks , metropolitan-area networks , and local-area networks.
现在有三种通过地域分类成的网络，广域网 城域网 局域网。
Wide-area networks (WANs) provide communications across a country or the entire world. The telephone network is the most pervasive example. It is often viewed as a single entity, even though it is made up of a variety of separate companies.
Whereas the phone system creates a voice connection between your phone and any other phones in the world,
the Internet—a world wide network of computer networks—makes it possible for you to connect your computer (equipped with the appropriate hardware and software)to a wide variety of remote computer. The remote computers may be thousands of miles away, yet you can search libraries of software, access news and other information, conduct business, and meet people with interests or hobbies similar to your own around the globe.
广域网提供了贯穿一个国家或者整个世界的通信，电话网络是一个最普通的例子，他经常被视为一个独立的实体，尽管他是由一类单独的公司建立的。
尽管手机系统创造了一个声音连接在你的电话和世界上任意一部电话之间。网络，一个世界的计算机网络，（配备适当的硬件和软件）使你的计算机连接到一个任意远的计算机成为了可能。远程计算机可能有数千英里之外，你还可以搜索库的软件，获取新闻和其他信息，进行业务，并满足人民的兴趣、联系世界各地有相同爱好的人。
The Internet isn‘t the only worldwide computer network. International companies have private networks to link offices in different countries together electronically to form 24-hour-a-day business operations. Commercial public networks like CompuServe, Prodigy, and America Online are also used by people around the world. As these networks have grown in popularity, they have begun to interconnect, creating a global collection of people and computers that are able to electronically communicate with one another.[3]
互联网并不是唯一的全球计算机网络，国际公司有专用的网络来连接，把不同国家的办公室连接到一起制定一个24小时都在运作的商业。公共商业网络，如??也同样被全世界的人使用，伴随着这些网络渐渐普及，他们开始互联，创造一个能让全球的人和计算机能以电子方式互相沟通。 Metropolitan-area Networks
Metropolitan-area networks (MANs) provide communications across and among major metropolitan areas such as New York, Chicago, or Los Angeles. Public-safety agencies such as police and fire departments, and dispatch-oriented companies, like Federal Express, operate and maintain their own private networks. They use MANs to allow their mobile ―out-of-office‖ workers to talk to and pass data back and forth to one another.
城域网提供通信在主要都市地区如纽约，芝加哥，或洛杉机。公共安全机构如警察和消防部门，和dispatch-oriented公司，像联邦快递，操作和维护他们自己的私人网络。他们用城域网使他们的移动电话和自由活动的工人交谈，来回传递数据到另一个。
more recent development is the public voice and data networks. An example you may be familiar with is the cellular telephone network, which is made possible by dividing a geographical area into hexagonal-shaped cells, each with a base station.[4] Each cell, which is approximately 10 miles(16 kilometers) across, has its own antenna. Like the public telephone network, public MANs eliminate the need for individuals and organizations to build and operate their own networks.
最近的发展是公共数据和语音网络。一个例子是你很熟悉的蜂窝电话网络，这可能是由一块地理区域划分为六角型细胞，每个基站。每一个细胞，这大约是10英里（16公里），有其自己的天线。像公共电话网，公共人的消除需要个人和组织的建立和经营自己的网络。 Local-area Networks
Local-area networks (LANs) provide communications within specific buildings or facilities. This type of network could be used, for example, in a company where computers are located in the sales, accounting, production, and purchasing departments. Each computer would handle the applications unique to its department. When communication among the computers is required, the computers pass data to one another over the network. For example, purchasing information must be passed to the accounting department for inclusion in the accounts payable system, or production-scheduling information must be passed to the purchasing department for use by the purchasing and inventory systems.
局域网（LAN）提供在特定的建筑物或设备通信。这种类型的网络可以使用，例如，在一个公司的电脑都在销售，财务，生产，采购部门。每台计算机都会处理本部门。当计算机之间需要进行通信，计算机通过数据在网络上彼此。例如，采购信息必须传送到会计部列入应付账款，或生产调度信息必须传送到采购部门采购和存货系统使用。
Local-area networks have many different topologies, or ways in which computer can be connected to the network. Today, the two most common topologies are called ring and bus networks.
局域网有多种不同的拓扑结构，使计算机可以连接到网络。今天，两种最常见的拓扑结构可以是环形网络和总线网络 Ring Networks
Computers on a ring network are hooked together one after the other to form one continuous ring. To access each computer, a piece of software called a token is passed around the ring. A token is the electronic equivalent of an envelope. It contains a destination address and a fixed amount of information. The most popular token method is called token passing, in which one token at a time passes from computer to computer and carries messages around the network.
在环形网络中的电脑，是一个一个连接起来的，来形成一个连续不断的环形。为了访问每台电脑，被称作令牌的一系列软件通过周围的环。令牌是电子设备中的信封，它包括了目的地地址和一些固定量的信息。最常用的令牌方法被称为令牌传递，其中一个令牌可以同时向网络中的其他计算机传递信息。
· Bus Networks
On a bus network computers are simply connected by a cable routed along a path in the vicinity of each device that must be connected to it. The most popular bus network is called Ethernet. Bus networks allow multiple messages to be sent simultaneously. This is often accomplished by ―listening‖ to the network to see if any computer is transmitting. If the network is free, the computer can send its data. If two computers accidentally send data at the same time, a collision occurs, and after detecting the collision, the computers wait a random amount of time to transmit again. This access control method goes by the name of Carrier Sense Multiple Access with Collision Detection(CSMA/CD).
在总线型网络上，计算机由一根电缆简单的连接，电缆的路由是按照附近每个必须连接到电缆上的设备所经的路径决定的。最流行的网络称为以太网。总线网络允许多个发送邮件的同时。这通常是通过―听‖到网络上看到的任何计算机发送。如果网络是免费的，计算机可以发送数据。如果电脑不小心发送数据的同时，发生碰撞，碰撞和检测后，电脑等待一个随机时间量再次传送。这种访问控制方法被称为冲突检测的载波侦听多路访问（多址/光盘）
The three major categories of networks are not mutually exclusive. A mobile worker using a portable computer can send a message to a coworker in a cross-country office because the networks can be linked through gateways—devices used to connect dissimilar networks. For example, the mobile worker‘s message might first be transmitted to a local cellular base station, switched to the telephone network and carried across the country to the coworker‘s office, then transferred via gateway into the office LAN.
三大类网络不是相互排斥的。移动工作者使用便携式计算机可以发送一个消息给同事在乡村办公室，由于网络可以通过网关设备用于连接不同网络。例如，移动工作者的消息可能会首先被传送到本地蜂窝基站，切换到电话网络和进行跨国家的同事的办公室，然后通过转移到办公局域网网关。
Local-area networks. Shown in this diagram are the two most common types of networks; token ring, and bus. The networks can be connected via a gateway so any two computers can communicate and share data. In addition, wireless links are possible, and it is possible to communicate to any computer in networks via a modem.
局域网络。图所示是最常见的类型的网络环形网络，总线网络。该网络可以连接通过一个网关，所以任何计算机通讯和共享数据。此外，无线连接是可能的，任何计算机通过调制解调器连接到网络。
Analog and Digital Transducers
As mentioned previously, considerable experience has been accumulated with analog transducers signal conditioning, signal; conditioning, A/D converters etc., and it is natural that the majority of current systems tend to use these techniques. However, there are a number of measuring techniques that are essentially digit in nature, and which when used as separate measuring instruments require some integral digital circuitry, such as frequency counters and timing circuits, to provide an indicator output. This type of transducer, if coupled to a computer does not necessarily require the same amount of equipment since much of the processing done by the integral circuitry could be programmed and performed and performed by the computer.
前面我们已经提到，人们在模拟转换器、信号调节器和A/D转换器等的使用上已经积累了大量的经验。因此，目前大部分的系统自然都采用这些技术。然而，还有很大一部分测量方法实质是数字的，在个别的测量仪中使用这些方法时，需要用到一些积分电路，如频率计数和计时电路等来提供指示输出。另外，如果把这种转换器和电脑相连的话，就可以省去一些器材；因为很多有积分电路执行的工作可以由计算机程序代为执行。
Collins classifies the signals handled in control and instrumentation systems as follows:
(1) Analog, in which the parameter of the system to be measured although initially derived in an analog form by a sensor is converted to an electrical analog, either by design or inherent in the methods adopted;
(2) Coded digital, in which a parallel digital signal is generated, each bit radix weighted according to some predetermined code. These are referred to in this book as direct digital transducers;
(3) Digital, in which a function, such as mean rate of a repetitive signal, is a measure of the parameter being measured. These are subsequently referred to as frequency domain transducers.
柯林斯把在控制和测量系统中处理的信号分为以下几类：
（1）模拟式。尽管系统的被测数最初通过传感器得到的是模拟信号，然后通过设计或采用原有的方法将模拟形式的信号转换成电模拟信号。
（2）数字码式。产生的信号是并行的数字信号，每一位的基数权重由预先编定的号码系统决定。在本书中这些仪器称作直接数字转换器。
（3）数字式。其中的函数是指测量参数时用到的量度标准，如对重复信号取平均值。这些仪器在后来称为频域转换器。
Some analog transducers are particularly suited to conversion to digital outputs using special techniques. The most popular of these are synchros, and similar devices, which produce a modulated output of a carrier frequency. For ordinary analog use, this output has to be demodulated to provide a signal whose magnitude and sign represent any conventional A/D technique to produce a digital output, there are techniques by which the synchro output can be converted directly to a digital output while providing a high accuracy and resolution, and at a faster rate than is possible in the A/D converter method.
特别地，一些模拟转换器适合用一些特别的技术来把模拟量转换成数字输出。其中最通用的方法是同步法和相似仪器的方法，即产生载波频率的调制输出的方法。在用作普通的模拟量输出仪器时，输出量必须经过解调。解调后输出的是直流信号，支流信号的大小和方向描述了转换器运动元件的偏移。虽然使用传统的A/D转换技术可以用来产生数字信号，在提供高精度时采用这些新技术将同步输出直接变为数字输出，比用A/D转换方法更快。
Direct digital transducers are, in fact, few and far between, since there do not seem to be any natural phenomena in which some detectable characteristic changes in discrete intervals as a result of a change of pressure, or change of temperature etc. There are many advantages in using direct digital transducers in ordinary instrumentation systems, even if computers are not used in the complete installation. These advantages are::
(1) The ease of generating, manipulating and storing digital signals, as punched tape, magnetic tape etc.; (2) The need for high measurement accuracy and discrimination;
(3) The relative immunity of a high level digital signal to external disturbances(noise);
(4) Ergonomic advantages in simplified data presentation(e.g. digital readout avoids interpretation errors in reading scales or graphs).
直接数字转换器实际上用得很少，因为在自然现象中很少有那种由温度变化、压力变化等因素作用而产生的可测量的离散的变化量。在普通的仪器系统中使用直接数字转换器有如下优点（即使在完成安装时不使用计算机）：
（1）容易产生、处理和存储信号，如打控带、磁带等； （2）高精度和高分辨率的需要；
（3）高介数字信号对外部噪声的抗干扰性；
（4）在简化数据描述时的人机工程学优势（例如：数字读出器能避免读刻度或图表时的判度错误）。 The most active development in direct digital transducer has been in shaft encoders, which are used extensively in machine tools and aircraft systems. High resolution and accuracies can be obtained, and these devices may be mechanically coupled to provide a direct digital output of any parameter which gives rise to a measurable physical displacement. The usual disadvantage of these systems is that the inertia of the instrument and encoder often limit the speed of response and therefore the operating frequencies.
在直接数字转换器中最能起作用的发展是轴编码器。轴编码器在机床和飞行系统中被广泛应用。利用这些设备能达到很高的精度和分辨率，而且这些设备能进行激动连接，给出任何可测量物理偏移的直接数字输出。这类系统通常的缺点是仪器的惯性及编码器限制了相应的速度，因而也限制了操作频率。
Frequency domain transducers have a special part to play in online systems with only few variables to be measured, since the computer can act as part of an A/D conversion system and use its own registers and clock for counting pulses or measuring pulse width. Access and process the transducer output. In designing such systems, consideration must be given to the computer time required to access and process the transducer output data.
频域转换器在线系统（测量量较少时）有着特殊的地位。因为计算机能担当A/D转换系统的部分工作，能用它自己的寄存器和时钟来计算脉冲和测量脉冲宽度。在这种系统的设计中必须考虑到计算机存取和处理转换器输出所需的时间。
Information systems combine several functions and devices. These systems provide an approach to the complex problem of measuring, using, and evaluating the mass of data and information produced by modern instrumentation, test, and control installations. Information and data handling systems are the next logical step from centralized control, graphic panels, and, multipoint recording systems. They present many data in logic form and balance the work performed by an operator and the automatic instrumentation system. They are widely used in industrial processes, test cells, and research and development laboratories to save time, increase accuracy of readings, reduce human error, and release skilled technicians for more important duties.
信息系统结合了许多功能和装置。这些系统提供了一个方法的复杂问题的测量，使用，和评价的质量数据和信息生产的现代仪器，测试，控制装置。信息和数据处理系统是一个合乎逻辑的步骤，从集中控制，图形板，和，多点记录系统。他们目前的许多数据在逻辑形式和平衡的工作由一个操作员和自动化仪表系统。它们被广泛应用于工业过程，测试细胞，并研究开发实验室，节省时间，提高数据的准确性，减少人为错误，并释放技术更重要的职责。
The following five major functions are performed by information handling systems: (1) automation measuring, the continuous and automatic switching of each input signal sequentially to the
measuring circuit and readout system;
(2) automatic logging, the continuous readout and display of all variables measured; (3) alarm monitoring, the continuous measurement and comparison of the measured variables with a
preset value or limit and an audio or visual indication or alarm of all off-normal(out-of-limit)points;
(4) data and alarm scanning, provides a sequential measurement and review of data and alarm points at a
central location with selective readout and display;
(5) low-speed and high-speed digital data handling systems, combine functions of measuring, logging,
monitoring, scanning, and simple computation (linearizing, square-root extraction, totalizing, scaling) with selection of a variety of analog and digital display forms.
以下五个主要功能是由信息处理系统：
（1）自动化测量，连续自动开关的每个输入信号顺序测量电路和读出系统； （2）自动记录，连续读出和显示所有变量测量；
（3）监控报警，连续测量和比较测量变量与预设值或限制和音频或视觉报警指示或所有非正常（极限）点；
（4）数据和报警扫描，提供了一个连续的测量和审查数据和报警点在一个中央位置有选择性地读出和显示；
（5）低速和高速数字数据处理系统，结合功能的测量，记录，监测，扫描，和简单的计算（线性，平方根提取，累计，缩放）选择各种模拟和数字显示形式。
The typical data handling system components and their functions are:
1. Transducers for converting measured variable into convenient electrical voltage or current input signal for
transmission to central room, e.g., thermocouples, resistance thermometers, electrical pressured transducers, stain gages, electrical flow transducers and pneumatic pressure to current converters.
2. Input selector switches to funnel many input information channels switching sequentially to measuring
circuit, e.g., telephone stepping switches, crossbar switches, mercury jet switches, electromechanical switching, electronic multiplexers and manual selector for operator control.
3. Signal conditioning: scaler to adjust some signals to common input value, amplifier to build up low-level
signals, linearizer to remove any nonlinearizer, special bridge balance circuit for certain transducers and analog to digital converter for those analog input signals which will be required for digital readout.
4. Measuring circuit, where the measured variable is actually measured. Servoo-perated null-balance
potentiometer, digital potentiometer with mercury-wetted relay switching, and electronic detector.
5. System programmer, the heart of the system, for it controls the whole system, establishes the routine of the
instrument, selects measuring circuits, switches point, initiates logging and alarms, and provides time information.
6. Readout programmer, actuates readout and display devices.
7. Readout and display, provides means of logging and displaying all variables, recording off-normal points,
recording computed values on analog strip charts, typewriter log sheets, digital display lights, paper punched tape, magnetic tape, oscillograph record, printed tape and punched card.
8. Input signal scaling, span adjustment, zero adjustment, alarm set-point adjustment (by mechanical means),
potentiometers, pinboards, and fixed resistors.
9. Special computation circuits for averaging, multiplying, dividing, and totalizing. These are functions anf
components incorporated in information systems. 典型的数据处理系统的组成及功能：
1。传感器转换成便于测量变量的电压或电流输入信号传输到中央室，例如，热电偶，电阻温度计，电压力传感器，应变片，电流量传感器、气动压力电流转换器。
2。输入选择器开关漏斗多输入信息渠道交换顺序测量电路，例如，电话交换机加强，交叉开关，水银射流开关，机电开关，电子多路复用器和手动选择操作控制。
3。信号调理：缩放调整信号共同的输入值，建立低水平信号放大器，线性化，消除任何非线性，特殊桥梁平衡电路若干传感器和模拟数字转换器的模拟输入信号，将所需的数字读出。
4。测量电路，在测量变量实际上是衡量。伺服传动阀，调零电位器，数字电位器与汞润继电器开关，电子探测器。
5。系统程序员，系统的心脏，它控制整个系统，建立常规的仪器，以测量电路，开关，启动日志和警报，并提供时间信息。
6。读出编程器，读出和显示设备的驱动。
7。读出和显示，提供了手段，记录和显示的所有变量，记录正常点，记录计算值模拟条图，打字机记录表，数字显示灯，纸打孔磁带，磁带，示波器记录，印刷带和穿孔卡片。
8。输入信号缩放，调整，调零，报警设定点调整（通过机械手段），电位器，插接板，固定电阻器。 9。特殊计算电路平均，乘法，分割，和整体性。这些功能和组成部分纳入信息系统。
According to the Encyclopedia Americana，a system is \by nature or man as to form an integral and complex whale\Mathematical systems theory is the study，of the interruptions and behavior of such an assemblage of \The abstract nature of systems theory is due to the fact that it is concerned with mathematical properties rather than the physical faun of the constituent parts.
按照美工大百科全书的解释，所谓系统就是指“一个各种物体的集合，格局其他性质或人的愿望而结合起来以致形成一个集中、复杂的整体”。数学中的系统理论，就是对这种由若干“物体”过程的集合，当其受到某些条件和输入作用的影响后的行为和阻断进行研究的一门学问。系统理论的抽象性质源于这样的一个事实：系统理论更关心物体组成的部件的数学性质而不是其物理形式。
Control theory is mare often concerned with physical applications. A control system is considered to he any system which exists for the purpose or regulating or controlling the flow of energy，information, money，or other quantities in some desired fashion. In more general terms，a control system is an interconnection of many components or functional units in such a way as to produce a desired result. In this book，control theory is assumed to encompass all questions related to design and analysis of control systems.
控制理论通常与实际应用有关。一般认为，控制系统是任意一个这样的系统，其目的是为了以某种期望的方式来调节或控制诸如能量，信息，资金等等物理量的流动。从更一般的意义上讲，控制系统就是一个按照一定方式由很多元件或功能单元构成的结合体，期目的是为了获得期望的结果。本书中假定控制理论包括所有与控制理论包括所有系统设计和分析问题有关的内容。
Fig. 37. 1 is a general representation of an open loop control system, the ingot or control u(t) is selected hayed on the goals for the system and all available a priori knowledge about the system, The input is in no way influenced by the output of the system，represented by y(t)，If unexpected disturbances act upon an open-loop system, or if its behavior is not completely understood，them the output will not behave precisely as expected.
图３７.１是对对开环控制系统的一般性表示。输入变量或控制作用ｕ（ｔ）是根据本系统的目标以及所有可获得的知识而选定的。输入变量绝不会受到ｙ（ｔ）所表示的系统输出变量的影响。如果有不期望的扰动作用在开环系统上，或者如果其行为不能完全掌握的话，则该系统的输出就不会完全如预期般动作。