This chapter describes the main components which, with the microprocessor, make up the microcomputer. The details given are sufficient to enable the engineer to use microcomputer effectively. This chapter discusses the structure of the microcomputer, including memory, the means of connecting to external devices, and power supplies. Programmable controllers are also briefly considered.
1.The microprocessor
The word “microprocessor” is popularly used when “microcomputer” is meant, in much the same way that “steam engine” is used for “steam locomotive”. To be exact, a microprocessor forms only part of a microcomputer. Microcomputers are based upon digital techniques, are very small and inexpensive enough to be used in limiteless engineering applications.
Microcomputers have to been programmed to operate in a required sequence. The fluid power engineer is usually the one who is most familiar with the control sequence of the equipment, so the programming is best done by him.
2.The microcomputer
The microprocessor is really quite useless on its own. It must be used with other devices. The basic elements are: microprocessor, to perform logic operation; memory, to hold programs and data; input/output device, to connect the external devices to the microcomputer; and power supply.
Such a system can be on a single board which comes complete, ready made and tested. The engineer has to interface the microcomputer with the fluid power system and provide a power supply and program. Other devices added to the basic microcomputer are known as peripherals and well-known examples are printers and visual display units.
3.Made of operation
The microprocessor is the “brain” of the microcomputer. It does its work by moving data or information between itself, the memory and the input/output device. It performs simple logical operations on data. The sequence in which it performs these operations is stored in memory in the form of a program.
Data are coded in binary form or in terms of binary digits. These are expressed mathematically in either 1s or 0s and called bits. Information is handled in units of a fixed number of bits. For example, an 8-bit microprocessor moves data in “bytes” or “words” or 8 bits, whereas a 16-bit microcomputer handles 16-bit words.
The rate at which a microprocessor executes instructions is governed a timing device. This timing device is often referred as the “clock” and is usually a quartz crystal (石英晶体). Typically one instruction is executed in 1 millionth of a second (1us).
4.The bus
The interconnecting structure of the microcomputer is called the “bus”. An 8-bit microprocessor will have 8 lines for transferring words of data, perhaps 16 lines for carrying a “memory address”, and a few lines control and power supply.
Data are transferred though the bus system to various devices. Information on locations of addresses are transferred via the address bus.
5. Memory
The memory of a microcomputer holds the program or programs currently being used and provides storage for information such as input values, results of calculations, etc. the engineer must consider two types of memory as these will invariably be present in all systems.
(1)Read only memory
Read only memory (ROM) comes in several types;
a.Mask programmed ROM in which the contents are “manufactured” giving a high initial cost but low unit cost. Hence it is used for volume products.
b.Programmable ROM (PROM) in which the user can determine the contents by burning our selected links in the circuit. It is used for medium volume products.
c.Erasable PROM (EPROM) in which the user inserts the contents electrically (using as EPROM programmer) and can erase the contents by means of ultraviolet light. It is used in low volume and developing application.
d.Electrically erasable PROM (EPROM). This holds its contents until erased by an electrical signal.
(2)Random access memory
In random access memory (RAM) of read/write memory the contents can be “written into” and “read from” by the microprocessor. It is used for temporary storage of programs and data since its contents are lost when the power supply is removed. It is known as volatile RAM.
RAM can come with a battery back-up. It will keep its contents for several years and in effect behave like ROM. It is then known as non-volatile ROM. Where possible, permanent programs should be in ROM cannot be corrupt by electrical interference.
Vocabulary
1.component n. 成分
2.locomotive n. 机车；火车头
3.peripheral n. 外围设备 adj. 外围的
4.interface n. 分界面；接触面
5.execute v. 执行
6.sequence n. 顺序
7.binary a.二进制的
binary digits 二进制数字
8.read only memory (ROM) 只读存储器
9.random access memory (RAM) 读写存储器
10.erasable a. 可擦去的
11.corrupt v. 破坏；腐烂
12.volatile a. 可丢失的
