单片机基础电气工程及其自动化毕业论文中英文翻译.doc

Fundamental of Single-chip MicrocomputersThe Single-chip Microcomputers is the culmination of both the development of the digital computer and the integrated circuit, arguably the two most significant inventions of the 20th century.These two types of architecture are found in single-chip microcomputers. Some employ the split program/data memory of the Harvard architecture, shown in Fig. 3-4A-1, others follow the philosophy, widely adopted for general-purpose computers and microprocessors, of making no logical distinction between program and data memory as in the Princeton architecture, shown in Fig. 3-4A-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 Fig. 3-4A-3.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 the 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 a device which can operate in a microprocessor mode by using some of the input/output lines as an address and data but 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 ; there can still be a significant saving in I/O and other chips compared to a conventional microprocessor based circuit. More exact replacements 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 the 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 a stack pointer or timer register are often logically incorporated into the RAM area. It is unnecessary to make a 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 handing of binary-coded decimal (BCD) data (for numerical displays, for example), hence it is common to find that the CPU is well adapted to handing 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 of a single line. These lines are readily interfaced to two-state devices such as switches, thermostats, solid-states relays, valves, motors, etc.Parallel Input/Output Parallel Input and output schemes vary somewhat in different microcomputers; 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 to 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 a 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 and synchronous communication schemes require protocols that provide framing (start and stop) information. This can be implemented as a hardware facility or U(S) ARP (Universal (synchronous) asynchronous receiver/transmitter) relieving the processor (and the applications programmer) of this low-level, time-consuming, detail. It is merely necessary to select 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 data in the appropriate format is then handled by the hardware circuit.Timer/Counter Facilities Many applications 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 the simplest programs. The preferred approach is to use a 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 preloadable 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 the elapsed time before the timer is restarted, which otherwise would be necessary if continuous precisely timed interrupts were required (as in a clock, for example). Sometimes associated with a 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 if external synchronization of microcomputer is required.单片机基础单片机是数字计算机和集成电路发展中的一个顶峰，而这二者可以说是20世纪的两项最有意义的发明。在单片机中有两种类型的体系结构。 一些采用的是分离的程序或数据存储器的哈佛建筑学结构，如下图3-4A-1所示，其他的一些根据原则，广泛采用通用计算机和微处理器，程序或数据存储器之间没有明确的区分开来的普林斯顿建筑学结构，如图3-4A-2所示。如图3-4A-3所示，概括地说一个单片机是把组成微型计算机的各个功能部件集成在一块芯片中，构成一个完整的微型计算机。只读程序存储器(ROM) ROM通常是为永久的应用程序。很多微型计算机的非易变性存储器和微型控制器供大容积应用使用，并且设备的制造要求在芯片的制造期间，记忆的内容永久地被保存。很清楚，因为变动不可能在制造以后，这就暗示着对只读存储器代码发展有了一定的限制。在这个发展过程中可能需要包含一个稳定开放的计算机系统以及使用强有力的硬件仿效能力的软件工具。有些制造商提供另外的ROM选择通过包含在他们的范围设备内有(或打算供用途使用)用户可编程序的记忆。这些最简单的方法通常是通过使用某些输入/输出线作为数据和地址总线访问在微处理器方式下运行的外部设备。作为单片机，此种设备可能在功能上表现为来自限制的I/O和改进的外部电路。在生产的集成电路中使用这些只读存储器附加设备是非常常见的，其容量在片内ROM的扩展是不容发展的; 与一条基于微处理机的常规电路相比，在输入/输出和其他芯片上的容量可能仍然比较小。 ROM设备的替换可以得到以与背负式的 EPROM (可擦除的可编程序存储器)的插口而不是ROM。EPROM比等效ROM设备昂贵，但是与提供的完全电路等值。 EPROM在设备上的低音量应用也是非常有吸引力的，因为它们提供了根据在片内的输入/输出，等等，以及为用户提供一个方便灵活的可编程性的单片机设备。随机存取存储器(RAM) RAM是用于存放所有在执行过程中的结果和中间数据。其存储容量的大小随设备型号的变化而变化，但是它有同样典型宽度(4，8，16位等等)作为处理器。特殊功能计数器，例如堆栈指针或定时器记数器经常在逻辑上被合并到RAM区域里。在微处理器系统情况下，RAM和处理器的记数器之间的区分是多余的，因为RAM和记数器通常在微型计算机没有完全被分离。中央处理单元(CPU) CPU是整个单片机的核心部件。 微型计算机和微型控制器的许多应用都介入了十进制(BCD)数据(例如为数字显示)，因此，共同发现了CPU能很好的适应传递此种数据。因为许多控制器的应用都介入了打开和关上这唯一的一条输出线或访问这条线路的数据，这也是共同性发现用于设置和重新设置各自的位记忆或输入/输出的好的设备。这些线很理所当然的成为了被连接的二状态设备例如开关、温箱、固态继电器、阀门、马达等等。并行的输入/输出 在不同的微型计算机系统中，其并行的输入/输出也不相同；在大多数