3电气工程及其自动化专业外文文献英文文献外文翻译plc方面2300.doc

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 Fig.3-5A-1, 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 Fig.3-5A-2. 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 unit CPU Data memory Fig.3-5A-1 A Harvard type Input Output unit CPU memory Fig.3-5A-2. A conventional Princeton computer Timer/ Counter System clock External Timing components Serial I/O ROM Reset Prarallel I/O RAM Interrupts 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 mem