1、 外文原文（复印件）
A: Fundamentals of Single-chip Microcomputer
The single-chip microcomputer is the culmination of both the development of the digital computer and the integrated circuit arguably the tow most significant inventions of the 20th century [1].
These tow types of architecture are found in single-chip microcomputer. Some employ the split program/data memory of the
Harvard architecture, shown in -5A, others follow the philosophy, widely adapted for general-purpose computers and microprocessors, of making no logical distinction between program and data memory as in the Princeton architecture, shown in -5A.
In general terms a single-chip microcomputer is characterized by the incorporation of all the units of a computer into a single device, as shown in Fig3-5A-3.
Program memory Input& Output CPU unit Data memory
-5A-1 A Harvard type
memory CPU
-5A. A conventional Princeton computer
Input& Output unit External Timer/ System Timing Counter clock components Serial I/O Reset ROM Prarallel I/O Interrupts RAM CPU Power Fig3-5A-3. Principal features of a microcomputer
Read only memory (ROM).ROM is usually for the permanent,
non-volatile storage of an applications program .Many microcomputers and microcontrollers are intended for high-volume applications and hence the economical manufacture of the devices requires that the contents of the program memory be committed permanently during the manufacture of chips . Clearly, this implies a rigorous approach to ROM code development since changes cannot be made after manufacture .This development process may involve emulation using a sophisticated development system with a hardware emulation capability as well as the use of powerful software tools.
Some manufacturers provide additional ROM options by including in their range devices with (or intended for use with) user programmable memory. The simplest of these is usually device which can operate in a
microprocessor mode by using some of the input/output lines as an address and data bus for accessing external memory. This type of device can behave functionally as the single chip microcomputer from which it is derived
albeit with restricted I/O and a modified external circuit. The use of these ROMless devices is common even in production circuits where the volume does not justify the development costs of custom on-chip ROM[2];there can still be a significant saving in I/O and other chips compared to a
conventional microprocessor based circuit. More exact replacement for ROM devices can be obtained in the form of variants with 'piggy-back' EPROM(Erasable programmable ROM )sockets or devices with EPROM instead of ROM 。These devices are naturally more expensive than equivalent ROM device, but do provide complete circuit equivalents. EPROM based devices are also extremely attractive for low-volume
applications where they provide the advantages of a single-chip device, in terms of on-chip I/O, etc. ,with the convenience of flexible user programmability.
Random access memory (RAM).RAM is for the storage of working
variables and data used during program execution. The size of this memory varies with device type but it has the same characteristic width (4,8,16 bits etc.) as the processor ,Special function registers, such as stack pointer or timer register are often logically incorporated into the RAM area. It is also common in Harard type microcomputers to treat the RAM area as a
collection of register; it is unnecessary to make distinction between RAM and processor register as is done in the case of a microprocessor system since RAM and registers are not usually physically separated in a microcomputer .
Central processing unit (CPU).The CPU is much like that of any
microprocessor. Many applications of microcomputers and microcontrollers involve the handling of binary-coded decimal (BCD) data (for numerical displays, for example) ,hence it is common to find that the CPU is well adapted to handling this type of data .It is also common to find good
facilities for testing, setting and resetting individual bits of memory or I/O since many controller applications involve the turning on and off of single output lines or the reading the single line. These lines are readily
interfaced to two-state devices such as switches, thermostats, solid-state relays, valves, motor, etc.
Parallel input/output. Parallel input and output schemes vary
somewhat in different microcomputer; in most a mechanism is provided to at least allow some flexibility of choosing which pins are outputs and which are inputs. This may apply to all or some of the ports. Some I/O lines are suitable for direct interfacing to, for example, fluorescent displays, or can provide sufficient current to make interfacing other components
straightforward. Some devices allow an I/O port to be configured as a system bus to allow off-chip memory and I/O expansion. This facility is potentially useful as a product range develops, since successive enhancements may become too big for on-chip memory and it is undesirable not to build on the existing software base.
Serial input/output .Serial communication with terminal devices is
common means of providing a link using a small number of lines. This sort of communication can also be exploited for interfacing special function chips or linking several microcomputers together .Both the common
asynchronous synchronous communication schemes require protocols that provide framing (start and stop) information .This can be implemented as a hardware facility or U(S)ART(Universal(synchronous) asynchronous receiver/transmitter) relieving the processor (and the applications programmer) of this low-level, time-consuming, detail. t is merely
necessary to selected a baud-rate and possibly other options (number of stop bits, parity, etc.) and load (or read from) the serial transmitter (or receiver) buffer. Serialization of the data in the appropriate format is then handled by the hardware circuit.
Timing/counter facilities. Many application of single-chip
microcomputers require accurate evaluation of elapsed real time .This can be determined by careful assessment of the execution time of each branch in a program but this rapidly becomes inefficient for all but simplest programs .The preferred approach is to use timer circuit that can
independently count precise time increments and generate an interrupt after a preset time has elapsed .This type of timer is usually arranged to be reloadable with the required count .The timer then decrements this value producing an interrupt or setting a flag when the counter reaches zero.
Better timers then have the ability to automatically reload the initial count value. This relieves the programmer of the responsibility of reloading the counter and assessing elapsed time before the timer restarted ,which otherwise wound be necessary if continuous precisely timed interrupts
were required (as in a clock ,for example).Sometimes associated with timer is an event counter. With this facility there is usually a special input pin ,that can drive the counter directly.
Timing components. The clock circuitry of most microcomputers
requires only simple timing components. If maximum performance is
required,a crystal must be used to ensure the maximum clock frequency is approached but not exceeded. Many clock circuits also work with a resistor and capacitor as low-cost timing components or can be driven from an external source. This latter arrangement is useful is external synchronization of the microcomputer is required.
WORDS AND TERMS
culmination n.顶点 spilt adj.分离的 volatile n. 易变的 commit v.保证 albeit conj.虽然 custom adj.定制的
variant adj.不同的
piggy-back adj.背负式的 socket n. 插座
B:PLC[1]
PLCs (programmable logical controller) face ever more complex
challenges these days . Where once they quietly replaced relays and gave an occasional report to a corporate mainframe, they are now grouped into cells, given new job and new languages, and are forced to compete against a growing array of control products. For this year's annual PLC technology update ,we queried PLC makers on these topics and more .
Programming languages
Higher level PLC programming languages have been around for some time ,but lately their popularity has mushrooming. \As Raymond Leveille, vice president & general manager, Siemens Energy &Automation .inc; Programmable controls are being used for more and more sophisticated operations, languages other than ladder logic become more practical, efficient, and powerful. For example, it's very difficult to write a
trigonometric function using ladder logic .\guages gaining acceptance include Boolean, control system flowcharting, and such function chart languages as Graphcet and its variation .And there's increasing interest in languages like C and BASIC.
PLCs in process control
Thus far, PLCs have not been used extensively for continuous process control .Will this continue \he feeling that I've gotten,\ays Ken Jannotta, manger, product planning, series One and Series Six product ,at GE Fanuc North America ,'is that PLCs will be used in the process industry but not necessarily for process control.\
Several vendors -obviously betting that the opposite will happen -have introduced PLCs optimized for process application .Rich Ryan, manger, commercial marketing, Allen-bradley Programmable Controls Div., cites PLCs's increasing use such industries as food ,chemicals ,and petroleum. Ryan feels there are two types of applications in which they're appropriate. \one,\ he says,\ where the size of the process control system that's being automated doesn't justify DCS[distributed control system].With the
starting price tags of chose products being relatively high, a programmable controller makes sense for small, low loop count application .The second is where you have to integrate the loop closely with the sequential
logical .Batch controllers are prime example ,where the sequence and maintaining the process variable are intertwined so closely that the
benefits of having a programmable controller to do the sequential logical outweighs some of the disadvantages of not having a distributed control system.\
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