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1、无锡科技职业学院 中英文翻译Computer control technology1 Computer structure and function This section introduces the internal architecture of a computer and describes how instructions are stored and interpreted and explains how the instruction execution cycle is broken down into its various components. At the mos
2、t basic level, a computer simply executes binary-coded results. For a general-purpose programmable computer, four necessary elements are the memory, central processing unit (CPU, or simply processor), an external processor bus, and an input/output system as indicated in Fig.3-1 A-1. Fig. 3-1A-1 Basi
3、c elements of a computer The memory stores instructions and data. The CPU reads and interprets the instructions, reads the data required by each instruction, executes the action required by the instruction, and stores the results back in memory. One of the actions that is required of the CPU is to r
4、ead data from or write data to an external device. This is carried out using the input/output system. The external processor bus is a set of electric conductors that carries data, address and control information between the other computer elements.1-1 The memory The memory of a computer consists of
5、a set of sequentially numbered locations. Each location is a register in which binary information can be stored. The “number” of a location is called its address. The lowest address is 0. The manufacturer defines a word length for the processor that is an integral number of locations long. In each w
6、ord the bits can represent either data or instructions. For the Intel 8086/87 and Motorola MC6800 microprocessors, a word is 16 bits long, but each memory location has only 8 bits and thus two 8-bit locations must be accessed to obtain each data word. In order to use the contents of memory, the proc
7、essor must fetch the contents of the right location. To carry out a fetch, the processor places (enables) the binary-coded address of the desired location onto the address lines of the external processor bus. The memory then allows the contents of the addressed memory location to be read by the proc
8、essor. The process of fetching the contents of a memory location does not alter the contents of that location. Instructions in memory Instructions stored in memory are fetched by the CPU and unless program branches occur, they are executed in the sequence they appear in memory. An instruction writte
9、n as a binary pattern is called a machine-language instruction. One way to achieve meaningful patterns is to divide up the bits into fields as indicated in Fig. 3-1A-2, with each field containing a code for a different type of information.Fig. 3-1A-2 Arrangement of program and data in memory Each in
10、struction in our simple computer can be divided up into four fields of 4 bits each. Each instruction can contain operation code (or opcode, each instruction has a unique opcode), operand address, immediate operands, branch address. In a real instruction set there are many more instructions. There is
11、 also a much large number of memory locations in which to store instructions and data. In order to increase the number of memory locations, the address fields and hence the instructions must be longer than 16 bits if we use the same approach. There are a number of ways to increase the addressing ran
12、ge of the microprocessor without increasing the instruction length: variable instruction field, multiword instructions, multiple addressing modes, variable instruction length. We will not discuss them in detail. Data in memory data is information that is represented in memory as a code. For efficien
13、t use of the memory space and processing time, most computers provide the capability of manipulating data of different lengths and representations in memory. The various different representations recognized by the processor are called its data types. The data types normally used are: bit, binary-cod
14、ed decimal digit (4-bit nibble, BCD), byte (8 bits), word (2 bytes), double word (4 bytes). Some processors provide instructions that manipulate other data types such as single-precision floating-point data types (32bits) and double-precision floating-point data types (64 bits). There is another typ
15、e of datacharacter data. It is also usually represented in 8 bits. Each computer terminal key and key combination (such as shift and control functions) on a standard terminal keyboard has a 7-bits code defined by the American Standard Code for Information Interchange (ASCII). Type of memory In the a
16、pplications of digital control system, we also concerned with the characteristics of different memory techniques. For primary memory, we need it to be stored information temporarily and to be written and got information from successive or from widely different locations. This type memory is called r
17、andom-access memory (RAM). In some case we do not want the information in memory to be lost. So we are willing to use special techniques to write into memory. If writing is accomplished only once by physically changing connections, the memory is called a read-only memory (ROM). If the interconnectio
18、n pattern can be programmed to be set, the memory is called a programmable read-only memory (PROM). If rewriting can be accomplished when it is necessary, we have an erasable programmable read-only memory (EPROM). An electronically erasable PROM is abbreviated EEPROM. 1-2 The CPU The CPUs job is to
19、fetch instructions from memory and execute these instructions. The structure of the CPU is shown in Fig. 3-1A-3. It has four main components: an arithmetic and logical unit (ALU), a set of registers, an internal processor bus and controller.Fig.3-1A-3 Central processing unit (CPU) These and other co
20、mponents of the CPU and their participation in the instruction cycle are described in the following sections. Arithmetic and Logical Unit (ALU) The ALU provides a wide arithmetic operations, including add, subtract, multiply, and divide. It can also perform Boolean logic operations such as AND, OR,
21、and COMPLEMENT on binary data. Other operations, such as word compares, are also available. The majority of computer tasks involve the ALU, but a great amount of data movement is required in order to make use of the ALU instructions. Registers A set of registers inside the CPU in used to store infor
22、mation. Instruction register When an instruction is fetched, it is copied into the instruction register, where it is decoded. Decoding means that the operation code is examined and used to determine the steps of the execution sequence. Programmers model of the CPU The collection of registers that ca
23、n be examined or modified by a programmer is called the programmers model of the CPU. The only registers that can be manipulated by the instruction set, or are visibly affected by hardware inputs or the results of operations upon data, are the registers represented in the model. Flag register The ex
24、ecution sequence is determined not only by the instruction but also by the results of the previous instructions. For example, if an addition is carried out in the ALU, data on the result of the addition (whether the result is positive, negative, or zero, for example) is stored in what is known as a
25、flag register, status register, or condition register. If the next instruction is a conditional branch instruction, the flag word is tested in that instruction to determine if a branch if a branch is required. Program counter (instruction pointer) The address of the next instruction is located in a
26、register called the program counter. Data registers When an instruction uses the registers to store data, the reference to the register in the instruction is called register addressing. The reasons of making use of the internal registers to store data are that they can make the instructions shorter
27、and make execution faster. Address registers The internal registers can also be used for the storage of address of data in memory data. In such a case, the instruction word contains a register number (i.e. a register address). In the register is contained the address of memory data to be used in the
28、 instruction. This form of addressing is called register indirect addressing. The contents of the register are said to point to the data in memory. Internal Processor Bus The internal processor bus moves data between internal register. A bus is a set of closely grouped electric conductors that trans
29、fers data, address, and control information between functional blocks of the CPU. Data from a source register can be passed to a destination register when both are enabled onto (connected to) the bus. Controller The controller provides the proper sequence of control signals for each instruction in a
30、 program cycle to be fetched from memory. A total program cycle comprises many instruction cycle, each instruction cycle can be divided up into its component machine cycles and each machine cycle comprises a number of clock cycle. In order to fetch an instruction, for example illustrated in Fig.3-1A
31、-4, the address in the program counter is placed on the address lines of the external bus (AB) at the onset of clock cycle C1. Simultaneously, using a code on the control lines of the bus (CB), the CPU informs all devices attached to the bus that an “opcode” fetch machine cycle is being executed by
32、the CPU. The memory allows the memory address to select the memory location containing the instruction. At C2 the controller places a “read” command onto the control bus which allows the memory data to be placed onto the data bus. The controller then gates the data into the instruction register and
33、removes the read command from the control bus in C3. At C4, the controller removes the address from the address bus and begins to decode the operation-code portion of the instruction to see what steps are required for execution. The decoding operation may take several more clock cycle at the end of
34、which the “opcode fetch” machine cycle. Fig. 3-1A-4 A timing diagram for operation-code fetch External attention requests It is often necessary to stop the normal instruction processing sequence. One type of external attention request is the reset request. In the case of an unrecoverable error, a co
35、mputer system may be required to reset itself .This would have the effect of initializing all important registers in the system and starting instruction execution from a standard memory location-usually location 0. An input that is more commonly activated during the normal course of events is the in
36、terrupt request. An interrupt request signal from an external device can cause the CPU to immediately execute a service subroutine which carries out the necessary actions. After completing the service subroutine, the processor will continue the task from which it was originally interrupted.The third
37、 type of input is the bus request, or direct memory access(DMA) request. It is possible to have a terminal interface that stores up all the characters in a line of text until it receives a carriage return. Then the interface requests the use of the system bus, at which time the complete line of data
38、 is transferred to memory as fast as possible. In this way the processor simply becomes inactive until the transfer is completed.1-3 Buses The bus is the most important communication system in a computer system. Under control of the CPU, a data source device and a data destination device are enabled
39、 onto(equivalent to being connected to) the bus wires for a short transmission. External processor bus The internal processor bus described in Sec. is connected to the external processor bus by a set of bus buffers located on the microprocessor integrated circuit. System bus The microcomputer board
40、can communicate with other boards by connecting its bus to an external system bus through a connector.1-4 Computer Input and Output A set of registers external to the CPU is associated with what is known as the input/output (I/O) system. The I/O system is connected to the external processor bus usin
41、g control, address, and data buses through an I/O registers in an interface. There are basically two ways that are used to address I/O register. In the first method, called I/O-mapped input/output, the operation code itself has special I/O instructions that address a numbered register in the interfa
42、ce called an I/O port. The second method of addressing I/O registers gives the I/O ports addresses that lie within the memory address range of the CPU. This is called memory-mapped I/O. Of course there must not be any memory locations at the same address as I/O locations. One of the benefits of the
43、memory-mapped approach is that the full range of memory addressing modes is available to the addressing of I/O registers.2 Fundamentals of Computer and Networks2-1 Organization of Computer System A computer is a fast and accurate symbol manipulating system that is organized to accept, store, and pro
44、cess data and produce output results under the direction of a stored program of instructions. This section explains why a computer is a system and how a computer system is organized. Key elements in a computer system include input, processing, and output devices. Lets examine each component of the s
45、ystem in more detail. Input Devices Computer system use many devices for input purpose. Some INPUT DEVICES allow direct human/machine communication, while some first require data to be recorded on an input medium such as a magnetizable material. Devices that read data magnetically recorded on specia
46、lly coated plastic tapes or flexible or floppy plastic disks are popular. The keyboard of a workstation connected directly to (or ONLINE to) a computer is an example of a direct input device. Additional direct input devices include the mouse, input pen, touch screen, and microphone. Regardless of th
47、e type of device used, all are components for interpretation and communication between people and computer systems. Central Processing Unit The heart of any computer system is the central processing unit (CPU). There are three main sections found in the CPU of a typical personal computer system: the
48、 primary storage section, the arithmetic-logic section, and the control section. But these three sections arent unique to personal computers. They are found in CPUs of all sizes. Output Device Like input units, output device are instruments of interpretation and communication between humans and computer system of all size. These device take output results from the CPU in machine-coded form and convert them into a form that can be used (a) by people (e.g. a printed and /or displayed report) or (b) as machine input in another processing cycle. In