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Basic computer
The basic components that make up a computer system: the CPU, memory, I/O, and the bus software thatsoftware requires a complete understanding of thiis in~ts material. ghsic operational design of a computer system is called its architecture.
John Von Neumann, a pioneer in computer design, gave the architecture of most computers in use today. A typical Von Neumann system has three major components: the central processing unit (or cPU), memory, and input/output (or I/O). The way a system designer these components impacts system performance. In VNA machines, like the 80x86 family, the CPU is where all the action takes place. All computations occur inside the CPU. Data and CPU instructions reside in memory by the CPU. To the CPU, most I/O devices look like memory because the CPU can stequired ta to anoutput device and read data from an input device. The major difference between memory and I/O locations is the fact that I/O locations are generally associated with external devices in the outside world.
1 the Motherboard
The motherboard is the main circuit board inside the PC which holds the processor, memory and expansion slots and connects directly or indirectly to every part of the PC (Fig 9.1 ). It's made up of a chipset (known as the "glue logic"), some code in ROM and the various interconnections or buses. PC designs today use many different buses to link their various components. Wide, high-speed buses are difficult and expensive to produce, the signals travel at such a rate that even distances of just a few centimeters cause timing problems; while the metal tracks on the circuit board act as miniature radio antennae, transmitting electromagnetic noise Fig 9.1 the motherboard that introduces interference with signals elsewhere in the system. For these reasons, PC design engineers try to keep the fastest buses confined to the smallest area of the motherboard and use slower, more robust buses, for other parts.
2 the System Bus
The system bus connects the various components of a VNA machine. The 80x86 family has
three major busses: the address bus, the data bus, and the control bus. A bus is a collection of wires
on which electrical signals pass between components in the system. These busses vary from processor to processor. However, each bus carries comparable information on all processors, for example, the data bus may have a different implementation on the 80386 than on the 8086, but both carry data between the processor, I/O, and memory.
1） the Data Bus
The 80x86 processors use the data bus to transfer data between the various components in a computer system. The size of this bus varies widely in the 80x86 family. Indeed, this bus defines -tP the "size" of the processor.
2）the Address Bus
The data bus on an 80x86 family processor transfers information between a particular memory location or I/O device and the CPU. The only question is, "Which memory location or I/O device? " The address bus answers that question.
To differentiate memory locations and I/O devices, the system designer assigns a unique memory address to each memory element and I/O device. When the software wants to access some particular memory location or I/O device, it places the corresponding address on the address bus. Circuitry associated with the memory or I/O recognizes this address and instructs the memory or I/O device to read the data from or place data on the data bus.
3）the Control Bus
The control bus is a collection of signals that control how the processor communicates with the rest of the system. Consider for a moment the data bus. The CPU sends data to memory and receives data from memory on the data bus. This prompts the question." Is it sending or receiving?" There are two lines on the control bus, read and write, which specify the direction of data flow. Other signals include system clocks, interrupt lines, status lines, and so on. The exact make up of the control bus varies among processors in the 80x86 families. However, some control lines are common to all processors and are worth a brief mention.
The read and write control the direction of data on the data bus. When both contain logic one, the CPU and memory, I/O is not communication with one another. If the read line is low (logiczero), the CPU is reading data from memory (that is, the system is transferring data from memory to the CPU). If the write line is low, the system transfers data from the CPU to memory.
3 Main Memory
The main memory is the central storage unit in a computer system. It is a relatively large and fast memory used to store programs and data during the computer operation. The principal technology used for the main memory is basedtg"~ A on semiconductor integrated circuits. Integrated circuits RAM (Read Random Memory) chips are available in two possible operation modes, staticand dynamic. The static RAM consists essentially of internal flip-flops that store the binary information. The stored information remains valid as long as power is applied to the unit. The dynamic RAM stores the binary information in the form of electric charges that are applied to the capacitors. The capacitors are provided inside the chip by MOS transistors. The stored charges on the capacitors tend to discharge with time and refreshing the dynamic memory must periodically recharge the capacitors. The dynamic RAM offers reduced power consumption and large storage capacity in a single memory chip. The static RAM is easier to use and has shorter read and write cycles.
4 BIOS (Basic Input/Output System)
1）Introduce to BIOS
One of the most common uses of Flash memory is for the basic input/output system of your computer, commonly known as the BIOS . The BIOS makes sure all the other chips, hard drives, ports and CPU function together.
The BIOS is special software that interfaces the major hardware components of your computer with the operating system. It is usually stored on a Flash memory chip on the motherboard, but sometimes the chip is another type of ROM (Read Only Memory).
2）What BIOS Does
The BIOS software has a number of different roles, BIOS uses Flash memory but its most important role is to load the operating system. When you turn on your computer and the microprocessor tries to execute its first instruction, it has to get that instruction from somewhere. It cannot get it from the operating system because the operating system is located on a hard disk, and the microprocessor cannot get to it without some instructions that tell it how. The BIOS provides those instructions. Some of the other common tasks that the BIOS performs include:
A power-on self-test (POST) for all of the different hardware components in the system to make sure everything is working properly.
Activating other BIOS chips on different cards and graphics cards often have their own BIOS chips. installed in the computer- For example, SCSI Providing a set of low-level routines that the operating system uses to interface to different hardware devices - It is these routines that give the BIOS its name. They manage things like the keyboard, the screen, and the serial and parallel ports, especially when the computer is booting. The first thing the BIOS does is check the information stored in a tiny (64 bytes) amount of RAM located on a CMOS chip. The CMOS setup provides detailed information particular to your system and can be altered as your system changes. The BIOS uses this information to modify or supplement its default programming as needed.
Interrupt handle/s ate-s'rria'll pieces ~f software that act as transl~tors between the hardware
components and the operating system. For example, when you press a key on your keyboard, the signal is sent to the keyboard interrupt handler, which tells the CPU what it is and passes it on to the operating system. The device drivers are other pieces of software that identify the base hardware components such as keyboard, mouse, hard drive and floppy drive. Since the BIOS is constantly intercepting signals to and from the hardware, it is usually copied, or shadowed, into RAM to run faster.
Future of portable computers
Steal a notebook computer from your competitor and you may be surprised to find that the data on its hard drive has self-destructed in your hands.
Giving central IT shops the ability to reach out to mobile computers - to destroy stolen information before it can be read, update application automatically or repair damage from rinses and other causes - is just one of the trends that will reshape the portable PC over the next five years.
Meanwhile, notebook processors will double in power every two years, to 12GHz in five years, predict industry observers, disks will shrink and may be replaced by solid-state memory. Displays will grow clearer, brighter and more energy-effitfient and may even unfold to desktop size.
The efficiency of batteries will improve, but perhaps not enough to keep up with power-hungry applications Such as multimedia and wireless communications.
Overall, the future of portable comtm~rs lies along two axes, as defined by the work habits of users.
Computer makers say they'll differentiate their products for those two groups. For the mostly office bound user, they plan to make portables with large screens, the most powerful CPUs, limited battery life and docking stations. Road warriors will get smaller and lighter units with all-day batteries but less powerful processors.
Tablets, a third category of portable PC, will soon join notebooks and subnotebooks. It's the middle ground between the traditional clamshell notebook design and the small form factor designs like PDAs.
A tablet PC is about the size of a legal pad and includes a digital pen for handwritten data entry and navigation. Its advocates say it will be just the thing for the most mobile workers. Including those who just don't like to type.
But naysayers( ~ff.~(~,~,,~ i~Jk,)point out that tablet- style computers have been tried flaws that vendors now claim to have overcome. Tablets will remain niche products at best, say these critics.
Microprocessor (Microcontroller)
The 8051 is a microprocessor and many derivative microcontrollers have the 8051. Thus, the ability to program an 8051 is an important skill for anyone who plans to develop products that will take advantage of microcontrollers.
The 8051 has three very general types of memory. To effectively program the 8051 it is necessary to have a basic understanding of these memory types.
They are: On-Chip Memory, External Code Memory, and External RAM.
On-Chip Memory refers to any memory (Code, RAM, or other) that physically exists on the microcontroller itself. On-chip memory can be of several types. External Code Memory is code (or program) memory that resides off-chip. This is often in the form of an external EPROM. External RAM is RAM memory that resides off-chip. This is often in the form of standard static RAM or flash RAM.
PLC
1) General
Programmable logic controllers (PLC) have been around recently. Their proven reliability in harsh environments and design to handle many inputs and outputs has made them the foundation of many factory automated systems.
The basic components of a PLC are the rack, power supply, CPU, and I/O modules.
Most PLCs have a separate rack and power supply to make them modular. For small systems we use a single small rack and power supply and for large systems we use multiple large racks and power supplies. Note that the power supply is intended to power the cards that plug into the rack and not for powering the sensors and actuators. The power for sensors and actuators should be powered using a separate, isolated power source (AC power or preferably a separate 24 V DC power supply).
2) Brick PLCs
The smallest PLCs sometimes have the CPU, rack, power supply and I/O all combined into a "brick" configuration. They are called "brick PLCs" because they are about the size of a brick. Manufacturers do this to reduce the total cost of the PLC as the cost of these "brick" PLCs
typical cost between $100 and $500. These PLCs do make sense in very simple and limited applications that will never be expanded in the future. Sometimes we would rather spend a little more money and have a modular system with future expansion capabilities.
3) PLC and Computer
Sometimes we do not use a typical PLC for the control engine. Typically what we do is:
If the application is small (less than 50 I/O), no databases (only a few choices), then use a PLC.
If the application is small, slow (response time greater than 50 milliseconds) and requires computer functionality (machine vision, networking, databases, multiple axis motion control, etc) we prefer to do the entire application in Visual Basic (VB) or C#.
If there are large amounts of I/O (over 100) or you need fast, real-time response, then you will probably want both - the PLC handling your real-time and direct I/O tasks and the computer handling the non-real-time tasks (such as databases, etc).
基本型计算机
组成一个计算机系统的基本部分是：中央处理器CPU、存储器、输入／输出端口和把它们连接在一起的总线。虽然你在编写软件程序时可以不考虑这些概念，但编写高性能的软件却需要对这些部件有一个完整的了解。
对一个计算机系统的基本设计被称为计算机的结构模型，冯·诺依曼，一个计算机设计的先驱，提出了今天所用的大部分计算机的结构模型。一个典型的冯·诺依曼系统有三个主要的部件：中央处理器(即CPU)、存储器及输入／输出口。一个系统中，设计这些部件的方法影响了系统的性能。在冯·诺依曼结构中，如80x 86系列计算机，所有的操作都在中央处理器中执行。所有的计算都在中央处理器内部进行，数据和指令储存在存储器，由中央处理器调用。对CPU而言，大量的输入／输出口就像存储器一样，因为CPU可以把数据存储在输出设备中，也可从输入设备中读入数据。存储器和输入／输出口主要的区别是输入／输出口通常是与(外部世界的)外部器件相连接的。
1 主板
主板是在计算机内部的主电路板，上面有中央处理器(CPU)、存储器和扩展槽，并与计算机的各个部分直接或非直接地相连(图9．1)。主板由芯片组(称为glue logic)、一些ROM中的代码和各种接口或总线组成。现在计算机中用各种不同的总线连接各种各样的部件。宽的、高速总线生产麻烦且成本高，(且)其信号的传输速度非常快，信号线只要有几厘米的传输距离就可能引起时间(延迟)问题；而电路板上的金属导线像微型无线电天线会发射电磁噪声，从而对系统中的信号产生干扰。因此，计算机(主板)设计者要把最高速的总线限制在主板的(某块)最小的面积中，而把较慢的、较粗的总线放在其他地方。
2 系统总线
系统总线连接冯·诺依曼结构中的各个部件，80x86系列计算机有三种主要的总线：地址线、数据线和控制线。总线是指一组在系统各个部件之间传递各种电信号的导线。对各种处理器所需要的总线不同。但是，对所有的处理器而言，每种总线都携带相应的信息，如803 86和8086有不同的数据总线(数目)，但都是在处理器、输入／输出口及存储器之间传递数据信息。
1) 数据总线
80x86系列处理器用数据总线在一个计算机系统的各种部分之间传递数据。在80x86系列中这组总线的数目是不同的，实际上，它决定了处理器的“大小"(即多少位数据的处理器)。
2) 地址总线
80x．86系列处理器中数据总线在中央处理器和一个特定的存储器位置或输入／输出口之间传递信息，但一个问题是：如何确定存储器或输入／输出口的位置?地址总线回答了这个问题。
对于不同的存储位置和输入／输出设备，系统的设计者指定一个唯一的存储地址。当软件想要访问一些指定的存储位置或输入／输出设备时，它把相应的地址值放在地址总线上，与存储器或输入／输出设备相连接的电路识别出这个地址，命令存储器或输入／输出设备从数据总线上读取数据或输出数据到数据总线上。
3) 控制总线
控制线是一组控制处理器如何与系统的其他部分通信的信号线的集合。再来看数据总线，CPU是通过数据总线把数据送到存储器中和从存储器中接收数据的，这就提出了一个问题“是送数据还是接收数据?"控制总线中有两根线：读和写，就是用来指定数据流动的方向的。其他的控制线包括系统时钟线、中断线、状态线等。在80x86系列处理器中控制总线的数目是各不相同的，然而，有些控制线是所有的处理器都有的，值得作简短介绍。
读和写控制线控制数据总线上数据流的方向，当这两根线都为逻辑l时，CPU和存储器、输入／输出口互相之间是不通信的，如果读控制线是低电平(逻辑O)，则CPU从存储器中读取数据(即系统是把数据从存储器中传送到CPU中的)，如果写控制线是低电平，系统把数据从CPU传送到存储器中。
3 主存(内存)
主存是一个计算机系统中的中心存储单元。它是一个相当大且存取速度很快的存储器，用来储存CPU操作时的程序和数据。主存主要采用半导体集成电路技术。有两种可用的集成RAM芯片，静态RAM和动态RAM。静态RAM本质上是用内部的触发器组成，用来储存二进制信息。只要芯片与电源相连，静态RAM储存的信息始终有效。动态的RAM以电容两极(充电)电荷的形式储存信息，芯片内的电容是由MOS管构成的。电容两端储存的电荷会随时间的延长而放电，要保持动态存储信息必须周期性地对电容再充电(刷新)。动态RAM功耗小，单一芯片的储存量大。静态RAM用起来方便且有较短的读和写周期(即读写速度快)。
4 BIOS(基本输入／输出系统)． ．
1) BlOS简介
闪存最主要的用途之一是储存计算机的基本输入／输出系统(通常称做BIOS)。BIOS使得所有其他芯片、硬件、端口和CPU蠢起工作。
BIOS是一种特殊的软件，是主要硬件与操作系统的接口软件，通常存储在主板的闪存芯片中，但有时也可能是存储在一种ROM芯片中。
2) BIOS的作用是什么
BIOS软件有很多不同的作用，但它最重要的作用是载入操作系统。当你开机时，微处理器开始执行第一条指令，就是储存在闪存中的BIOS。微处理器不能执行操作系统，因为操作系统存储在硬盘上，没有指令CPU不能从硬盘上载入操作系统，BIOS提供了这些指令。BIOS还提供了一些其他指令，如：
电源自检(POST)用来检查系统中各个硬件是否工作正常。
激活(调用)计算机中其他不同卡上BIOS芯片中的程序，如SCSI(接口卡)和图像处理卡本身自带BIOS芯片。
操作系统与不同硬件接口的低级处理程序，就是这些低级程序调用各种设备。尤其是计算机启动时这些程序管理键盘、显示屏、串行和并行接口等设备。
BIOS所做的第二件事是检查储存在一微小(64字节)RAM(一个CMOS芯片)中的信息，CMOS给出了你系统的设置信息，当你系统改变时可以改变CMOS设置，BIOS要根据这些信息调整或补充它的默认程序。
中断处理是一小段软件程序，就像是硬件与操作系统之间的翻译。例如当你在键盘上按下一个键，信号就调用了键盘的中断处理程序，告诉CPU是什么键并送给操作系统。设备驱动是另外的软件程序，它识别基本的硬件，如键盘、鼠标、硬盘和软盘驱动器。因为BIOS是不断地从硬件接收信号和输出信号给硬件的，所以为了运行更快，(计算机启动后)一般把BIOS复制到RAM中。
便携式计算机的未来
(在未来)你从竞争对手那里偷了一台笔记本电脑，你会惊讶地发现你手中(电脑)硬盘上的数据已经自我销毁。
把信息中心的(控制)能力延伸到移动计算机——在被偷的信息读出之前就销毁掉、应用程序自动升级或修复因病毒和其他原因造成的损坏，这还只是今后五年便携式PC机将采用的新性能的趋势之一。
同时，业内的观察家们预测，笔记本电脑的处理器速度每两年就翻一番，五年内将达到1 2G．Hz，磁盘会缩小，有可能会被固态存储器替代。显示器会更清晰、更亮、更省电，甚至还可能展开成台式机的尺寸。
电池的效率将改进，但可能跟不上多媒体和无线通信等这类耗电多的应用程序的改进步伐。
总体上，按用户工作的习惯，便携式计算机的未来将沿两个方向发展。
计算机制造商说，他们将为两类人群设计不同的产品。对于大部分时间在办公室工作的用户，他们计划制造具有大屏幕、最强大CPU、使用时间有限的电池和带有外接口(以扩展硬盘等)的便携机。而流动工作的人将得到较小、较轻，具备能工作一天的电池，但CPU功能不太强的便携机。
平板式电脑不久将加入到笔记本电脑和类笔记本电脑中，成为第三类便携式PC机，它介于传统的翻盖式笔记本电脑设计与像PDA(个人数字助理、商务通)那样的小外形尺寸设计之间。
平板式PC机的尺寸约为一般便签纸大小，包括一支数字笔，用于输入手写数据以及(指点)导航。喜欢它的人说，这就是大多数流动工作者所要的东西，包括那些不喜欢用键盘的人。
但是反对者指出，平板式的计算机以前就试验过，但有缺陷(虽然现在供应商声称已经克服了这些缺陷)。这些批评者说，平板机在最好的情况下也只是(使用面)很窄的产品。
单片机(微控制器)
805l是一种单片机，现在许多开发的微控制器中都有805 1，因此对一个想要用微处理器开发产品的人来说掌握805 1编程技术是很重要的。
8051有三种存储器，为了掌握805 1编程(技术)需要了解这些基本的存储类型。
它们是片内存储器、外部程序存储器和外部数据存储器。
片内存储器是指单片机芯片内自带的存储器(程序、数据和其他类型)，片内存储器可能有几种形式。外部程序存储器是代码(程序)存储器，是外接的EPROM芯片。外部RAM存储器也是外部芯片，通常是静态RAM或闪存RAM芯片。
PLC(可编程逻辑控制器)
1) 概述
可编程逻辑控制器(PLC)近年来到处可见，PLC在恶劣工作环境中工作的可靠性和可以处理许多输A．／输出结点的设计使它们成为许多工厂自动化系统的基本(设备)。
PLC的主要部件是插件箱、电源模块、CPU模块和I／O模块。
许多PLC有分开的插件箱和电源，可以(根据需要)组合，对小系统可用一个小插件箱和一个电源，对大的系统我们用多个大插件箱和多个电源，注意电源只能对插件箱中的卡供电，并不能对传感器和执行器(如电动机)供电。传感器和执行器要由另外的隔离电源供电(交流电源或独立24V直流电源)。
2) 一体式PLC
微小型PLC有时把CPU、插件箱、电源和输入／输出接口组合成一体，称为砖式PLC(文中译做一体式)，因为其大小像一块砖。制造商为了减小总成本，生产这种一体式PLC，一体式PLC成本仅在l OO～500美元。这种PLC很简单且使用范围也有限(以后永远不能扩展接口)。有时我们宁可多花一些钱购买一个将来可以扩展的模块化系统。
3) PLC与计算机
有时用PLC做控制设备并不一定合适，通常的选择是：
如果要控制的设备是少量的，少于50个I／O接口，不需要数据库(只有一些控制选择)就用一个PLC。
如果控制设备是少量的、慢速的(响应时间大于50ms)并需要计算机功能(可视化、网络、数据库、多轴运动控制等)，我们宁可用VB或C样的完整程序(即选用计算机)。
如果有很多I／O(超过1 OO个)接口，或需要快速、实时响应，则PLC与计算机两个都需要，PLC处理实时响应和直接输入／输出任务，计算机处理非实时任务(如数据库等)。