機械工程及自動化專業(yè)外文翻譯-工程中的單片機

1、外文原文:Microprocessors in EngineersThe developme nt of the microprocessor duri ng the 1970s brought about a revoluti on in engin eeri ng desig n. The in dustrial revoluti on at the tur n of the nin etee nth cen tury heralded the developme nt of the mach ines which could replace physical drudgery by me

2、cha ni cal means. Apart from a few excepti ons, however, these mach ines required manual supervisi on because the problem of con trolli ng this mecha ni cal power was not at all straightforward.Many types of automatic con trol systems have appeared duri ng the twen tieth cen tury, based on electr on

3、ic, mecha ni cal, hydraulic and fluidic prin ciples. In each case the desig n tech niq ues have bee n similar because each comp onent of the system usually con tributes a sin gle well defi ned fun cti on to the system behavior.The microprocessor represe nts a fun dame ntally differe nt approach to t

4、he desig n of a system. Its physical form is quite simple and reliable, con sisti ng of a few gen eral-purpose elements which can be programmed to make the system function as required. It is the controlling program which must be designed to give the system the required behavior, and which will con t

5、ai n comp onents and subassemblies just like any other ki nd of engin eeri ng. The program, or software, is just of the engin eered system as the physical hardware, but it is much less susceptible to failure, provided that it is designed properly.The idea of programmed systems is not n ew; electro n

6、ic computers have bee n in existe nee for many decades. However, it has take n the developme nt of the large scale in tegrated circuit-the silic on chip-to produce computers which are cheap, rugged, and reliable eno ugh to be in corporated into engin eeri ng desig ns as comp onen ts. The techniques

7、of software design are well known to computer scientists and it is not surpris ing that the prin ciples of good engin eeri ng desig n an d software engin eeri ng are esse ntially those of good engin eeri ng desig n. We shall see that engin eeri ng desig n using software allows systems to be desig ne

8、d more easily tha n using more conven ti onal tech niq ues.It is the comb in ati on of developme nts in electr onic device tech no logy with those in computer tech no logy which has en abled the microprocessor to be produced, and these tech no logies have Con verged to produce the micro-electro nic

9、in dustry which we see today.More rece nt developme nts in in tegrated circuit tech no logy have led to the in troductio n of microprocessor small computers fabricated using relatively few in tegrated circuit components. In fact an entire microprocessor can be made as a single chip. At the heart of

10、any computer is a Cen tral Process ing Unit or CPU, and the corresp onding heart of the microprocessor is MPU(Micro-Processor Un it), which is simply a CPU implemented on a silicon chip. Its processing power is greater than that of its giant predecessors and yet it is cheap and robust eno ugh to be

11、treated as simply ano ther engin eeri ng comp onent.The microprocessor was con ceived as a device which could be programmed in a very flexible fashion to give almost any desired behavior by means of a list of electronic in structi ons. Usi ng a microprocessor invo Ives program ming skill in produci

12、ng these lists of in struct ions as well as more conven ti onal electr onic and mecha ni cal desig n tech niq ues. As its n ame suggests, the microprocessor is orga ni zed in much the same way as a conven ti onal computer; in deed, it may be regarded as thenatural outcome of the evolution” of the co

13、mputer from its earliest days.Systems Us ing MicroprocessorsElectronic systems are used for handling information in the most general sense; this in formatio n may be teleph one conv ersatio n, in strume nt readi ng or a compa nys acco un ts, but in each case the same main types of operati on are inv

14、o Ived: the process ing, storage and tran smissi on of in formatio n. In conven ti onal electro nic desig n these operati ons are comb ined at the function level: for example a coun ter, whether electr onic or mecha ni cal, stores the curre nt count and in creme nts it by one as required. A system s

15、uch as an electro nic clock which employs coun ters has its storage and process ing capabilities spread throughout the system because each coun ter is able to store and process nu mbers.Prese nt day microprocessor based systems depart from this conven ti onal approach by separati ng the three fun ct

16、i ons of process ing, storagejnd tran smissi on into differe nt sections of the system. This partitioning into three main functions was devised by Von Neuma nn duri ng the 1940s, and was not con ceived especially for microcomputers. Almost every computer ever made has bee n desig ned with this struc

17、ture, and despite the enormous range in their physical forms, they have all been of essentially the same basic desig n.In a microprocessor based system the process ing will be performed in the microprocessor itself. The storage will be by means of memory circuits and the com muni cati on of in forma

18、ti on 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 coun ti ng in a microprocessor based clock because the time would be stored in the memory and in creme nted at regular in te

19、rvals by the microprocessor. However, the software which defi ned the systems behavior would con tai n sect ions that performed as coun ters. The appare ntly rather abstract approach to the architecture of the microprocessor and its associated circuits allows it to be very flexible in use, since the

20、 system is defined almost entirely in software. The design process is largely one of software engin eeri ng, and the similar problems of con structi on and maintenance which occur in conven ti onal engin eeri ng are encoun tered whe n produci ng software.How these three sect ions within a microcompu

21、ter are conn ected in terms of the com muni cati on of in formatio n within the mach ine. The system is con trolled by the microprocessor which supervises the tran sfer of in formatio n betwee n itself and the memory and in put/output sect ions. The external conn ecti ons relate to the rest (that is

22、, the non-computer part) of the engin eeri ng system.Although on ly one storage sect ion has bee n show n in the diagra m, in practice two dist inct types of memory RAM and ROM are used. In each case, the word memory israther in appropriate since a computer memory is more like a fili ng cab inet in

23、con cept ; information is stored in a set of numbered boxes and it is refereneed by the serial number of the boxinquestion.Microcomputers use RAM (Ra ndom Access Memory) into which data can be writte n and from which data can be read aga in whe n n eeded. This data can be read back from the memory i

24、n any seque nee desired, and not n ecessarily the same order in which it was written, hence the expression randomaccess memory. Another type of ROM (Read On ly Memory) is used to hold fixed patter ns of in formatio n which cannot be affected by the microprocessor; these patter ns are not lost whe n

25、power is removed and are n ormally used to hold the program which defi nes the behavior of a microprocessor based system.ROMs can be read like RAMS, but unlike RAMS they cannot be used to store variable in formatio n. Some ROMs have their data patter ns put in duri ng manu facture, while others are

26、programmable by the user by means of special equipme nt and are called programmable ROMs. The widely used programmable ROMs 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 el

27、ectrically without the n eed for ultraviolet light, which are called Electrically Erasable Programmable Read Only Memories, EEPROMS.The microprocessor processes data un der the con trol of the program, con trolli ng the flow of in formatio n to and from memory and in put/output devices. Some in put/

28、output devices are gen eral-purpose types while others are desig ned for con trolli ng special hardware such as disc drives or con troll ing in formatio n tran smissi on to other computers. Most types of I/O devices are programmable to some exte nt, allowi ng differe nt modes of operati on, while so

29、me actually contain special-purpose microprocessors to permit quite complex operati ons to be carried out without directly involving the main microprocessor.The microprocessor, memory and in put/output circuit may all be contained on the same in tegrated circuit provided that the applicati on does n

30、ot require too much program or data storage. This is usually the case in low-cost application such as the controllers used in microwave ove ns and automatic washi ng mach in es. The use of sin gle package allows con siderable cost sav ings to be made whe n articles are manu factured in large qua nti

31、ties. As tech no logy develops, more and more powerful processors and larger and larger amounts of memory are being in corporated into sin gle chip microcomputers with resulting saving in assembly costs in the final products. For the foreseeable future, however, it will continue to be necessary to i

32、nterconnect a number of integrated circuits to make a microcomputer whe never larger amounts of storage or in put/output are required.Another major engineering application of microcomputers is in process control. Here the prese nee of the microcomputer is usually more appare nt to the user because p

33、rovisi on is no rmally made for program ming the microcomputer for the particular applicati on. In process con trol applicati ons the ben efits of fitt ing the en tire system on to a sin gle chip are usually outweighed by the high desig n cost invo Ived, because this sort of equipment is produced in

34、 smaller quantities. Moreover, process controllers are usually more complicated so that it is more difficult to make them as single integrated circuits. Two approaches are possible; the con troller can be impleme nted as a gen eral-purpose microcomputer rather like a more robust versi on of a hobby

35、computer, or as a packaged system, desig ned for replaci ng con trollers based on older tech no logies such as electromagnetic relays. In the former case the system would probably be programmed in conventional programming Ianguages such as the ones to be introduced later, while in the other case a s

36、pecial-purpose Ian guage might be used, for example one which allowed the function of the controller to be described in terms of relay interconnections. In either case programs can be stored in RAM, which allows them to be altered to suit changes in applicati on, but this makes the overall system vu

37、ln erable to loss of power uni ess batteries are used to en sure con ti nuity of supply. Alternatively programs can be stored in ROM, in which case they virtually become part of the electr onic hardware and are ofte n referred to as firmware.More sophisticated process con trollers require mini compu

38、ters for their implementation, although the use of large scale integrated circuits blurs the distinction betwee n mini- and microcomputers. Products and process con trollers of various kinds represent the majority of present-day microcomputer applications, the exact figures depe nding on ones ierpre

39、tati on of the word product. Virtually all engin eeri ng and scie ntific uses of microcomputers can be assig ned to one or other of these categories.Microcomputer In terfaceA microcomputer in terface con verts in formatio n betwee n two forms. Outside the microcomputer the in formatio n han dled by

40、an electro nic system exists as a physical signal, but within the program, it is represented numerically. The function of any in terface can be broke n dow n in to a nu mber of operati ons which modify the data in some way, so that the process of conv ersi on betwee n the exter nal and internal form

41、s is carried out in a nu mber of steps.This can be illustrated by means of an example such as that of Figure 1, which shows an in terface betwee n a microcomputer and a tran sducer produc ing a con ti nu ously variable an alog sig nal. Tran sducers ofte n produce very small output requiri ng amplifi

42、cati on, or they may gen erate sig nals in a form that n eeds to be con verted aga in before being han dled by the rest of the system. For example, many tran sducers have variable resista nee which must be conv erted to a voltage by a special circuit. This process of con vert ing the tran sducer out

43、put into a voltage sig nal which can be conn ected to the rest of the system is called signal conditioning. In the example of Figure .1, the signal con diti oning secti on tran slates the range of voltage or curre nt sig nals from the tran sducer to one which can be converted to digital form by an a

44、nalog-to-digital converter.An an alog-to-digital con verter (ADC) is used to convert a continu ously variable signal to a corresponding digital form which can take any one of a fixed number of possible binary values. If the output of the tran sducer does not vary con ti nu ously, no ADC is n ecessar

45、y .In this case the sig nal con diti oning sect ion must con vert the incoming sig nal to a form which can be conn ected directly to the n ext part of the in terface, the input/output section of the microcomputer itself.The I/O sect ion converts digital on /off voltage sig nals to a form which can b

46、e prese nted to the processor via the system buses. Here the state of each in put line, whether it is 6n” or off ”，is indicated by a corresponding 1” or 0”.Inthe an alog in puts which have bee n conv erted to digital form, the patter ns of ones and zeros in the internal representation will form bina

47、ry numbers corresponding to the qua ntity being conv erted.The raw nu mbers from the in terface are limited by the desig n of the in terface circuitry and they often require converter and scaling to produce values suitable for use in the main program. For example, the in terface might be used to con

48、vert temperatures in the ran ge-20 to +50 degrees, but the nu mbers produced by an 8-bit con verter will lie in the range 0 to 255. Obviously it is easier from the programmers point of view to deal directly with temperature rather tha n to work out the equivale nt of any give n temperature in terms

49、of the nu mbers produced by the ADC. Every time the in terface is used to read a tran sducer, the same operatio ns must be carried out to con vert the in put nu mber into a more convenient form. Additi on ally, the operati on of some in terfaces requires con trol sig nals to be passed betwee n the m

50、icrocomputer and comp onents of the in terface. For these reasons it is normal to use a subroutine to look after the detailed operation of the in terface and carry out any scali ng an d/or con verter which might be n eeded.Output in terfaces take a similar form (Fig.2), the obvious differe nce being

51、 that here the flow of in formatio n is in the opposite directi on; it is passed from the program to the outside world. In this case the program may call an output subrout ine which supervisesthe operati on of the in terface and performs the scali ng nu mbers which may be n eeded for a digital-to-an

52、alog converter (DAC). This subroutine passes information in turn to an output device which produces a corresp onding electrical sig nal, which could be conv erted into an alog form using a DAC. Fin ally the sig nal is con diti oned (usually amplified) to a form suitable for operati ng an actuator.Fi

53、g.2 Output InlerfeceDigital In terface CircuitsThe signals used within microcomputer circuits are almost always too small to be conn ected directly to the outside world and some ki nd of in terface must be used to tran slate them to a more appropriate form. The desig n of secti on of in terface circ

54、uits is one of the most importa nt tasks facing the engin eer wish ing to apply microcomputers. We have see n that in microcomputers in formatio n is represe nted as discrete patter ns of bits; this digital form is most useful when the microcomputer is to be connected to equipme nt which can only be

55、 switched on or off, where each bit might represe nt the state of a switch or actuator.Care must be taken when connecting logic circuits to ensure that their logic levels and curre nt rati ngs are compatible. The output voltages produced by a logic circuit are normally specified in terms of worst ca

56、se values when sourcing or sinking the maximum rated currents. Thus V6h is the guaranteed minimum high voltage when sourcing the maximum rated high output current Ioh, while Vol is the guaranteed minimum low output voltage when sinking the maximum rated low output current Ol. There are corresp ondin

57、g specificati ons for logic in puts which specify the minimum in put voltage which will be recog ni zed as a logic high state Vih, and the maximum in put voltage which will be regarded as a logic low state Vil.For in put in terface, perhaps the main problem facing the desig ner is that of electrical

58、 noise. Small noise signals may cause the system to malfunction, while larger amounts of no ise can perma nen tly damage it. The desig ner must be aware of these dan gers from the outset. There are many methods to protect in terface circuits and microcomputer from various hinds of no ise. Follow ing

59、 are some examples:In put and output electrical isolati on betwee n the microcomputer system and exter nal devices using an opt-isolator or a tran sformer.Removing high frequency noise pulses by a low pass filter and Schmitt-trigger.Protect ing aga inst excessive in put voltages using a pair of diod

60、es to power supply reversibly biased in no rmal direct ion,For output in terface, parameters Vh, Vol, Ioh and Iol of a logic device are usually much to low to allow loads to he conn ected directly, and in practice an exter nal circuit must be conn ected to amplify the curre nt and voltage to drive a