毕业设计工程中的微型计算机外文文献

1、内蒙古工业大学本科毕业设计说明书Microcomputers in EngineeringSystems Using MicroprocessorsThe development of the microcomputer during the 1970s brought about a revolution in engineering design. The industrial revolution at the turn of the nineteenth century heralded the development machines which replaced physical

2、drudgery by the mechanical mean. A major engineering application of microcomputers is in process control. The provision is normally made for programming the microcomputer for the particular application.Electronic systems are used for handing information in the most general sense; This information ma

3、y be telephone conversation, instrument reading or a companys accounts, but in each case the same main types of operation are involved: the processing, storage and transmission of information. In conventional electronic design these operations are combined at the function level: for example a counte

4、r, whether electronic or mechanical, stores the current count and increments it by one as required. A system such as an electronic clock which employs counters has its storage and processing capabilities spread throughout the system because each counter is able to store and process numbers.Present d

5、ay microprocessor based systems depart from this conventional approach by separating the three functions of processing, storage, and transmission into different sections of the system. This partitioning into three main functions was devised by Von Neumann during the 1940s, and was not conceived espe

6、cially for microcomputers. Almost every computer ever made has been designed with this structure, and despite the enormous range in their physical forms, they have all been of essentially the same basic design.In a microprocessor based system the processing will be performed in the microprocessor it

7、self. The storage will be by means of memory circuits and the communication of information into and out of the system will be by means of special input/output (I/O) circuits. It would be impossible to identify a particular piece of hardware which performed the counting in a microprocessor based cloc

8、k because the time would be stored in the memory and incremented at regular intervals by the microprocessor. However, the software which defined the systems behavior would contain sections that performed as counters. The apparently rather abstract approach to the architecture of the microprocessor a

9、nd its associated circuits allows it to be very flexible in use, since the system is defined almost entirely in software. The design process is largely one of software engineering, and the similar problems of construction and maintenance which occur in conventional engineering are encountered when p

10、roducing software.Figure 1.1 illustrates how these three sections within a microcomputer are connected in terms of the communication of information within the machine. The system is controlled in terms of the communication of information within the machine. The system is controlled by the microproce

11、ssor which supervises the transfer of information between itself and the memory and input/output sections. The external connections relate to the rest (that is, the non-computer part) of the engineering system.Fig.1.1 Three Sections of a Typical MicrocomputerAlthough only one storage section has bee

12、n shown in the diagram, in practice two distinct types of memory RAM and ROM are used. In each case, the word memory is rather inappropriate since a computer memory is more like a filing cabinet in concept; information is stored in a set of numbered boxes and it is referenced by the serial number of

13、 the box in question.Microcomputers use RAM (Random Access Memory) into which data can be written and from which data can be read again when needed. This data can be read back from the memory in any sequence desired, and not necessarily the same order in which it was written, hence the expression ra

14、ndom access memory. Another type of ROM (Read Only Memory) is used to hold fixed patterns of information which cannot be affected by the microprocessor; these patterns are not lost when power is removed and are normally used to hold the program which defines the behavior of a microprocessor based sy

15、stem. ROMs can be read like RAMs, but unlike RAMs they cannot be used to store variable information. Some ROMs have their data patterns put in during manufacture, while others are programmable by the user by means of special equipment and are called programmable ROMs. The widely used programmable RO

16、Ms are erasable by means of special ultraviolet lamps and are referred to as EPROMs, short for Erasable Programmable Read Only Memories. Other new types of device can be erased electrically without the need for ultraviolet light, which are called Electrically Erasable Programmable Read Only Memories

17、, EEPROMs.Microcomputer InterfaceA microcomputer interface converts information between two forms. Outside the microcomputer the information handled by an electronic system exists as a physical signal, but within the program, it is represented numerically. The function of any interface can be broken

18、 down into a number of operations which modify the data in some way, so that the process of conversion between the external and internal forms is carried out in a number of steps.This can be illustrated by means of an example such as that of Figure 1.2, which shows an interface between a microcomput

19、er and a transducer producing a continuously variable analog signal. Transducers often produce very small output requiring amplification, or they may generate signals in a form that needs to be converted again before being handled by the rest of the system. For example, many transducers have variabl

20、e resistance which must be converted to a voltage by a special circuit. This process of converting the transducer output into a voltage signal which can be connected to the rest of the system is called signal conditioning. In the example of Figure 1.2, the signal conditioning section translates the

21、range of voltage or current signals from the transducer to one which can be converted to digital form by an analog-to-digital converter.Fig.1.2 Input InterfaceAn analog-to-digital converter (ADC) is used to convert a continuously variable signal to a corresponding digital form which can take any one

22、 of a fixed number of possible binary values. If the output of the transducer does not vary continuously, no ADC is necessary. In this case the signal conditioning section must convert the incoming signal to a form which can be connected directly to the next part of the interface, the input/output s

23、ection of the microcomputer itself.The I/O section converts digital “on/off” voltage signals to a form which can be presented to the processor via the system buses. Here the state of each input line, whether it is “on” or “off”, is indicated by a corresponding “1” or “0”. In the analog inputs which

24、have been converted to digital form, the patterns of ones and zeros in the internal representation will form binary numbers corresponding to the quantity being converted.The “raw” numbers from the interface are limited by the design of the interface circuitry and they often require linearization and

25、 scaling to produce values suitable for use in the main program. For example, the interface might be used to convert temperatures in the range -20 to +50 degrees, but the numbers produced by an 8-bit converter will lie in the range 0 to 255. Obviously it is easier from the programmers point of view

26、to deal directly with temperature rather than to work out the equivalent of any given temperature in terms of the numbers produced by the ADC. Every time the interface is used to read a transducer, the same operations must be carried out to convert the input number into a more convenient form. Addit

27、ionally, the operation of some interfaces requires control signals to be passed between the microcomputer and components of the interface. For these reasons it is normal to use a subroutine to look after the detailed operation of the interface and carry out any scaling and/or linearization which mig

28、ht be needed.Output interfaces take a similar form (Fig 1.3), the obvious difference being that here the flow of information is in the opposite direction; it is passed from the program to the outside world. In this case the program may call an output subroutine which supervises the operation of the

29、interface and performs the scaling numbers which may be needed for a digital-to-analog converter (DAC). This subroutine passes information in turn to an output device which produces a corresponding electrical signal, which could be converted into analog form using a DAC. Finally the signal is condit

30、ioned (usually amplified) to a form suitable for operating an actuator.Fig.1.3 Output Interface IN this project, it is used Pressure Transmitters and Speed Transmitters.Pressure and Pressure Transmitters Pressure arises when a force is applied over an area Provided the force is one Newton (N) and un

31、iformly over the area of one square meter(m2)，the pressure has been designated one Pascal(Pa=N/m2).Pressure is a universal processing condition. It is also a condition of life on this planet：we live at the bottom of an atmospheric ocean that extends upward for many miles. This mass of air has weight

32、，and this weight pressing downward causes atmospheric pressure. Water，a fundamental necessity of life，is supplied to most of US under pressure. In the typical process plant，pressure influences boiling point temperatures，condensing point temperatures，process efficiency，costs，and other important facto

33、rs. The measurement and control of pressure，or lack of it-vacuum-in the typical process plant is critical.The working instruments in the plant usually include simple pressure gauges，precision recorders and indicators，and pneumatic and electronic pressure transmitters. A pressure transmitter makes a

34、pressure measurement and generates either a pneumatic or electrical signal output that is proportional to the pressure being sensed.In the process plant，it is impractical to locate the control instruments out in the place near the process. It is also true that most measurements are not easily transm

35、itted from some remote location. Pressure measurement is an exception，but if a high pressure of some dangerous chemical is to be indicated or recorded several hundred feet from the point of measurement，a hazard may be from the pressure or from the chemical carried.To eliminate this problem，a signal

36、transmission system was developed. This system is usually either pneumatic(air pressure)or electrical. Using the transmission system，it wilt be possible to install most of the indicating，recording，and control instruments in one location. This makes it practical for a minimum number of operators to r

37、un the plant efficiently.When a pneumatic transmission system is employed，the measurement signal is converted into pneumatic signal by the transmitter scaled from 0 to 100 percent of the measured value. This transmitter is mounted close to the point of measurement in the process. The transmitter out

38、putair pressure for a pneumatic transmitteris piped to the recording or control instrument. The standard output range for a pneumatic transmitter is 20 to 100kPa，which is almost universally used.When an electronic pressure transmitter is used，the pressure is converted to electrical signal that may b

39、e current or voltage. Its standard range is from 4 to 20mA DC for current signal or from 1 to 5V DC for voltage signal. Nowadays，another type of electrical signal. which is becoming common，is the digital or discrete signal. The use of instruments and control systems based on computers or microproces

40、sors is forcing increased use of this type of signal.Sometimes it is important for analysis to obtain the parameters that describe the sensor/transmitter behavior. The gain is fairly simple to obtain once the span is known. Consider an electronic pressure transmitter with a range of 0600kPa.The gain

41、 is defined as the change in output divided by the change in input. In this case，the output is electrical signal(420mA DC)and the input is process pressure(O600kPa).Thus the gainKr =(20mA-4mA)/(600kPa-0kPa)=16mA/600kPa=0.27mA/kPaSpeed transmitter Speed transmitter is usually used closed-speed magnet

42、ic circuit reluctance belt speed sensor, which by the induction gear, sensors teeth, with induction coil, such as magnets composed. When the sensor gear shaft and measured connection with rotational axis, the induction of the gear teeth on movement sensors, air-gap between the two gears in the size

43、of the cyclical changes, changes have caused reluctance principle of electromagnetic induction can be induced potential. If the gear teeth to Z, measured shaft equipped with pulleys, its diameter D, the belt speed of V, while According to this belt can be the speed. FOR this, the speed of strap can

44、be received. 工程中的微型计算机微处理器化系统20世纪70年代的微型计算机发展引起了工程的一场革命。在19世纪之初的工业革命宣布了用机械工具代替繁重的体力劳动的机器有了进步。微计算机的一个主要工程应用是在过程控制中，装置是按特定的应用情况由微机编程实现。广义地说，电子系统是用于处理信息的，这种信息可以是电话交谈、仪器读数或企业帐户，但是各种情况下都涉及相同的主要操作：信息处理、存储和传送。在常规的电子设计中，这些操作都是以功能平台方式组合起来的，例如计数器，无论是电子的还是机械的，都要存储当前值，并按要求将该值增1。诸如采用计数器的电子钟之类的任一系统要使其存储和处理能力遍布整个系

45、统，因为每个计数器都能存储和处理一些数字。当前微处理器化系统与上述的常规方法不同，它将处理、存储和传输三个功能分离形成不同的系统单元。这种形成三个主要单元的分离方法是冯诺依曼在20世纪40年代所设想出来的，并且是针对微计算机的设想。从此几乎所有制成的计算机都是用这种结构设计的，尽管包含宽广的物理形式，从根本上来说它们均是具有相同的基本设计。在微处理器化系统中，处理是由微处理器本身完成的。存储是利用存储器电路，而进入和出自系统的信息传输则是利用特定的输入/输出（I/O）电路。要在一个微处理器化时钟中找出执行计数功能的一个特殊硬件是不可能的，因为时间存储在存储器中，而在固定的时间间隔下由微处理器控

46、制增值。但是，规定系统运转过程的软件包含实现计数器功能的单元。由于系统几乎完全由软件所定义，所以对微处理器结构和其辅助电路这种看起来非常抽象的处理方法使其在应用时非常灵活。这种设计过程主要是软件工程，而且在生产软件时，就会遇到产生于常规工程中相似的构造和维护问题。图1.1 典型微计算机的三个部分图1.1显示出了微型计算机中这三个单元是如何按照机器中的信息通信方式而联接起来的。该系统由微处理器控制，它管理自己与存储器和输入/输出单元的信息传输。外部的连接与工程系统的其余部分（即非计算机部分）有关。尽管图中显示的只有一个存储单元，实际中有RAM和ROM两种不同的存储器被使用。由于概念上的计算机存储

47、器更像一个公文柜，上述的“存储器”一词时非常不恰当的；信息存放在一系列已标号的“箱子”中，而且可按问题由“箱子”的序列号进行信息的参考定位。微计算机常使用RAM（随机存取存储器），在RAM中数据可被写入，并且在需要时可被再次读出。这种数据能以任一所希望的次序从存储器中读出，不必按写入时的相同次序，所以有“随机”存取存储器。另一类型ROM（只读存储器）用来保持不受微处理器影响的固定的信息标本；这些标本在电源切断后不会丢失，并通常用来保存规定微处理器化系统运转过程的程序。ROM可像RAM一样被读取，但与RAM不一样的是不能用来存储可变的信息。有些ROM在制造时将其数据标本放入，而另外的则可通过特殊

48、的设备由用户编程，所以称为可编程ROM。被广泛使用的可编程ROM可利用特殊紫外线灯擦除，并被称为EPROM，即可擦除可编程只读存储器的缩写。另有新类型的器件不必用紫外线灯而用电擦除，所以称为电可擦除可编程只读存储器EEPROM。微机接口微机接口实现两种信息形式的交换。在计算机之外，由电子系统所处理的信息以一种物理信号形式存在，但在程序中，它是用数字表示的。任一接口的功能都可分为以某种形式进行数据变换的一些操作，所以外部和内部形式的转换是由许多步骤完成的。用图1.2所示的情况为例加以说明，图中展示了微计算机和产生连续变化模拟信号的传感器之间的接口。传感器产生的信号常很小，需要放大，或者产生的信号

49、和形式被系统的其他部分处理之前需要再次转换。举例来说，许多传感器具有电阻变化，这必须由一专门电路转换成电压。这种将传感器输出转换成电压信号，并与系统的其他电路相连接的过程，称为信号调理。如图1.2所示例子中，信号调理部分将源自传感器的电压或电流信号范围转换成可用模拟-数字转换器变成数字形式的信号范围。图1.2 输入接口一个模拟-数字转换器（ADC）用来将连续变化信号变成相应的数字量，这数字量可是可能的二进制数值中的一固定值。如果传感器输出不是连续变化的，就不需模拟-数字转换。这种情况下，信号调理单元必须将输入信号变换成为另一信号，也可直接与接口的下一部分，即微计算机本身的输入输出单元相连接。输入/输出单元将数字“开/关”电压信号转换成能通过系统总线传送到计算机的信号形式。这里每一根线的状态，无论是“开”或是“关”，用相应得“1”或“0”表示。对于已经转换成数字形式的模拟输入量，内