电气自动化专业毕业设计方案书英文翻译.docVIP

Computer control technology 1 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 most 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 Basic 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 read 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 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 word 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 processor 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 line