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单片机毕业设计外文翻译

单片机毕业设计外文翻译
单片机毕业设计外文翻译

单片机

1 单片机定义

单片机也被称为微控制器(Microcontroller Unit),常用英文字母的缩写MCU 表示单片机,它最早是被用在工业控制领域。单片机由芯片内仅有CPU的专用处理器发展而来。最早的设计理念是通过将大量外围设备和CPU集成在一个芯片中,使计算机系统更小,更容易集成进复杂的而对体积要求严格的控制设备当中。INTEL的Z80是最早按照这种思想设计出的处理器,从此以后,单片机和专用处理器的发展便分道扬镳。

早期的单片机都是8位或4位的。其中最成功的是INTEL的8031,因为简单可靠而性能不错获得了很大的好评。此后在8031上发展出了MCS51系列单片机系统。基于这一系统的单片机系统直到现在还在广泛使用。随着工业控制领域要求的提高,开始出现了16位单片机,但因为性价比不理想并未得到很广泛的应用。90年代后随着消费电子产品大发展,单片机技术得到了巨大提高。随着INTEL i960系列特别是后来的ARM系列的广泛应用,32位单片机迅速取代16位单片机的高端地位,并且进入主流市场。而传统的8位单片机的性能也得到了飞速提高,处理能力比起80年代提高了数百倍。目前,高端的32位单片机主频已经超过300MHz,性能直追90年代中期的专用处理器,而普通的型号出厂价格跌落至1美元,最高端的型号也只有10美元。当代单片机系统已经不再只在裸机环境下开发和使用,大量专用的嵌入式操作系统被广泛应用在全系列的单片机上。而在作为掌上电脑和手机核心处理的高端单片机甚至可以直接使用专用的Windows和Linux操作系统。

单片机比专用处理器更适合应用于嵌入式系统,因此它得到了最多的应用。事实上单片机是世界上数量最多的计算机。现代人类生活中所用的几乎每件电子和机械产品中都会集成有单片机。手机、电话、计算器、家用电器、电子玩具、掌上电脑以及鼠标等电脑配件中都配有1-2部单片机。而个人电脑中也会有为数不少的单片机在工作。汽车上一般配备40多部单片机,复杂的工业控制系统上甚至可能有数百台单片机在同时工作!单片机的数量不仅远超过PC机和其他计算的总和,甚至比人类的数量还要多。

2 单片机历史

单片机诞生于20世纪70年代末,经历了SCM、MCU、SOC三大阶段。

(1)SCM即单片微型计算机(Single Chip Microcomputer)阶段,主要是寻求最佳的单片形态嵌入式系统的最佳体系结构。“创新模式”获得成功,奠定了SCM与通用计算机完全不同的发展道路。在开创嵌入式系统独立发展道路上,Intel公司功不可没。

(2)MCU即微控制器(Micro Controller Unit)阶段,主要的技术发展方向是:不断扩展满足嵌入式应用时,对象系统要求的各种外围电路与接口电路,突显其对象的智能化控制能力。它所涉及的领域都与对象系统相关,因此,发展MCU的重任不可避免地落在电气、电子技术厂家。从这一角度来看,Intel逐渐淡出MCU的发展也有其客观因素。在发展MCU方面,最著名的厂家当数Philips公司。

Philips公司以其在嵌入式应用方面的巨大优势,将MCS-51从单片微型计算机迅速发展到微控制器。因此,当我们回顾嵌入式系统发展道路时,不要忘记Intel 和Philips的历史功绩。

(3)嵌入式系统阶段,单片机是嵌入式系统的独立发展之路,向MCU阶段发展的重要因素,就是寻求应用系统在芯片上的最大化解决;因此,专用单片机的发展自然形成了SOC化趋势。随着微电子技术、IC设计、EDA工具的发展,基于SOC的单片机应用系统设计会有较大的发展。因此,对单片机的理解可以从单片微型计算机、单片微控制器延伸到单片应用系统。

3单片机的应用领域

目前单片机渗透到我们生活的各个领域,几乎很难找到哪个领域没有单片机的踪迹。导弹的导航装置,飞机上各种仪表的控制,计算机的网络通讯与数据传输,工业自动化过程的实时控制和数据处理,广泛使用的各种智能IC卡,民用豪华轿车的安全保障系统,录像机、摄像机、全自动洗衣机的控制,以及程控玩具、电子宠物等等,这些都离不开单片机。更不用说自动控制领域的机器人、智能仪表、医疗器械了。因此,单片机的学习、开发与应用将造就一批计算机应用与智能化控制的科学家、工程师。

单片机广泛应用于仪器仪表、家用电器、医用设备、航空航天、专用设备的智能化管理及过程控制等领域,大致可分如下几个范畴:

(1)在智能仪器仪表上的应用

单片机具有体积小、功耗低、控制功能强、扩展灵活、微型化和使用方便等优点,广泛应用于仪器仪表中,结合不同类型的传感器,可实现诸如电压、功率、频率、湿度、温度、流量、速度、厚度、角度、长度、硬度、元素、压力等物理量的测量。采用单片机控制使得仪器仪表数字化、智能化、微型化,且功能比起采用电子或数字电路更加强大。例如精密的测量设备(功率计,示波器,各种分析仪)。

(2)在工业控制中的应用

用单片机可以构成形式多样的控制系统、数据采集系统。例如工厂流水线的智能化管、电梯智能化控制、各种报警系统,与计算机联网构成二级控制系统等。

(3)在家用电器中的应用

可以这样说,现在的家用电器基本上都采用了单片机控制,从电饭褒、洗衣机、电冰箱、空调机、彩电、其他音响视频器材、再到电子秤量设备,五花八门,无所不在。

(4)在计算机网络和通信领域中的应用

现代的单片机普遍具备通信接口,可以很方便地与计算机进行数据通信,为在计算机网络和通信设备间的应用提供了极好的物质条件,现在的通信设备基本上都实现了单片机智能控制,从手机,电话机、小型程控交换机、楼宇自动通信呼叫系统、列车无线通信、再到日常工作中随处可见的移动电话,集群移动通信,无线电对讲机等。(5)单片机在医用设备领域中的应用

单片机在医用设备中的用途亦相当广泛,例如医用呼吸机,各种分析仪,监护仪,超声诊断设备及病床呼叫系统等等。

(6)在各种大型电器中的模块化应用

某些专用单片机设计用于实现特定功能,从而在各种电路中进行模块化应用,而不要求使用人员了解其内部结构。如音乐集成单片机,看似简单的功能,微缩在纯电子芯片中(有别于磁带机的原理),就需要复杂的类似于计算机的原理。如:音乐信号以数字的形式存于存储器中(类似于ROM),由微控制器读出,转化为模拟音乐电信号(类似于声卡)。

在大型电路中,这种模块化应用极大地缩小了体积,简化了电路,降低了损坏、错误率,也方便于更换。

(7)单片机在汽车设备领域中的应用

单片机在汽车电子中的应用非常广泛,例如汽车中的发动机控制器,基于CAN 总线的汽车发动机智能电子控制器,GPS导航系统,abs防抱死系统,制动系统等等。

此外,单片机在工商,金融,科研、教育,国防航空航天等领域都有着十分广泛的用途。

4 单片机介绍

单片机又称单片微控制器,它不是完成某一个逻辑功能的芯片,而是把一个计算机系统集成到一个芯片上。相当于一个微型的计算机,和计算机相比,单片机只缺少了I/O设备。概括的讲:一块芯片就成了一台计算机。它的体积小、质量轻、价格便宜、为学习、应用和开发提供了便利条件。同时,学习使用单片机是了解计算机原理与结构的最佳选择。

单片机内部也用和电脑功能类似的模块,比如CPU,内存,并行总线,还有和硬盘作用相同的存储器件,不同的是它的这些部件性能都相对我们的家用电脑弱很多,不过价钱也是低的,一般不超过10元即可用它来做一些控制电器一类不是很复杂的工作足矣了。我们现在用的全自动滚筒洗衣机、排烟罩、VCD等等的家电里面都可以看到它的身影!它主要是作为控制部分的核心部件。

它是一种在线式实时控制计算机,在线式就是现场控制,需要的是有较强的抗干扰能力,较低的成本,这也是和离线式计算机的(比如家用PC)的主要区别。

单片机是靠程序运行的,并且可以修改。通过不同的程序实现不同的功能,尤其是特殊的独特的一些功能,这是别的器件需要费很大力气才能做到的,有些则是花大力气也很难做到的。一个不是很复杂的功能要是用美国50年代开发的74系列,或者60年代的CD4000系列这些纯硬件来搞定的话,电路一定是一块大PCB板!但是如果要是用美国70年代成功投放市场的系列单片机,结果就会有天壤之别!只因为单片机的通过你编写的程序可以实现高智能,高效率,以及高可靠性!

单片机内部也用和电脑功能类似的模块,比如CPU,内存,并行总线,还有和硬盘作用相同的存储器件,不同的是它的这些部件性能都相对我们的家用电脑弱很多,不过价钱也是低的,一般不超过10元即可......用它来做一些控制电器一类不是很复杂的工作足矣了。我们现在用的全自动滚筒洗衣机、排烟罩、VCD等等的家电里面都可以看到它的身影!它主要是作为控制部分的核心部件。

它是一种在线式实时控制计算机,在线式就是现场控制,需要的是有较强的抗干扰能力,较低的成本,这也是和离线式计算机的(比如家用PC)的主要区别。

由于单片机对成本是敏感的,所以目前占统治地位的软件还是最低级汇编语言,它是除了二进制机器码以上最低级的语言了,既然这么低级为什么还要用呢?很多高级的语言已经达到了可视化编程的水平为什么不用呢?原因很简单,就是单片机没有家用计算机那样的CPU,也没有像硬盘那样的海量存储设备。一个可视化高级语言编写的小程序里面即使只有一个按钮,也会达到几十K的尺寸!对于家用PC的硬盘来讲没什么,可是对于单片机来讲是不能接受的。单片机在硬件资源方面的利用率必须很高才行,所以汇编虽然原始却还是在大量使用。一样的道理,如果把巨型计算机上的操作系统和应用软件拿到家用PC上来运行,家用PC的也是承受不了的。

可以说,二十世纪跨越了三个“电”的时代,即电气时代、电子时代和现已进入的电脑时代。不过,这种电脑,通常是指个人计算机,简称PC机。它由主机、键盘、显示器等组成。还有一类计算机,大多数人却不怎么熟悉。这种计算机就是把智能赋予各种机械的单片机(亦称微控制器)。顾名思义,这种计算机的最小系统只用了一片集成电路,即可进行简单运算和控制。因为它体积小,通常都藏在被控机械的“肚子”里。它在整个装置中,起着有如人类头脑的作用,它出了毛病,整个装置就瘫痪了。现在,这种单片机的使用领域已十分广泛,如智能仪表、实时工控、通讯设备、导航系统、家用电器等。各种产品一旦用上了单片机,就能起到使产品升级换代的功效,常在产品名称前冠以形容词——“智能型”,如智能型洗衣机等。现在有些工厂的技术人员或其它业余电子开发者搞出来的某些产品,不是电路太复杂,就是功能太简单且极易被仿制。究其原因,可能就卡在产品未使用单片机或其它可编程逻辑器件上。

4.1 AT89C51介绍

8 位AT89C51 CHMOS 工艺单片机被设计用于处理高速计算和快速输入/输出。MCS51 单片机典型的应用是高速事件控制系统。商业应用包括调制解调器,电动机控制系统,打印机,影印机,空调控制系统,磁盘驱动器和医疗设备。汽车工业把MCS51 单片机用于发动机控制系统,悬挂系统和反锁制动系统。AT89C51 尤其很好适用于得益于它的处理速度和增强型片上外围功能集,诸如:汽车动力控制,车辆动态悬挂,反锁制动和稳定性控制应用。由于这些决定性应用,市场需要一种可靠的具有低干扰潜伏响应的费用-效能控制器,服务大量时间和事件驱动的在实时应用需要的集成外围的能力,具有在单一程序包中高出平均处理功率的中央处理器。拥有操作不可预测的设备的经济和法律风险是很高的。一旦进入市场,尤其任务决定性应用诸如自动驾驶仪或反锁制动系统,错误将是财力上所禁止的。重新设计的费用可以高达500K 美元,如果产品族享有同样内核或外围设计缺陷的话,费用会更高。另外,部件的替代品领域是极其昂贵的,因为设备要用来把模块典型地焊接成一个总体的价值比各个部件高几倍。为了缓和这些问题,在最坏的环境和电压条件下对这些单片机进行无论在部件级别还是系统级别上的综合测试是必需的。Intel Chandler 平台工程组提供了各种单片机和处理器的系统验证。这种系统的验证处理可以被分解为三个主要部分。系统的类型和应用需求决定了能够在设备上执行的测试类型。

4.2 AT89C51提供以下标准功能:

4k 字节FLASH 闪速存储器,128 字节内部RAM,32 个I/O 口线,2 个16 位定时/计数器,一个5 向量两级中断结构,一个全双工串行通信口,片内振荡器及时钟电路。同时,AT89C51 降至0Hz 的静态逻辑操作,并支持两种可选的节电工作模式。空闲方式体制CPU 的工作,但允许RAM,定时/计数器,串行通信口及中断系统继续工作。掉电方式保存RAM 中的内容,但振荡器体制工作并禁止其他所有不见工作直到下一个硬件复位。

4.3 引脚功能说明

·Vcc:电源电压

·GND:地

·P0 口:P0 口是一组8 位漏极开路型双向I/O 口,也即地址/数据总线复用。作为输出口用时,每位能吸收电流的方式驱动8 个TTL 逻辑门电路,对端口写“1”可作为高阻抗输入端用。在访问外部数据存储器或程序存储器时,这组口线分时转换地址(低8 位)和数据总线复用,在访问期间激活内部上拉电阻。在Flash 编程时,P0 口接受指令字节,而在程序校验时,输出指令字节,校验时,要求外接上拉电阻。

·P1 口:P1 是一个带内部上拉电阻的8 位双向I/O 口,P1 的输出缓冲级可驱动(吸收或输出电流)4 个TTL 逻辑门电路。对端口写“1”,通过内部的上拉电阻

把端口拉到高电平,此时可作输入口。作为输入口使用时,因为内部存在上拉电阻,某个引脚被外部信号拉低时会输出一个电流(IIL)。Flash 编程和程序校验期间,P1 接受低8 位地址。

·P2 口:P2 是一个带有内部上拉电阻的8 位双向I/O 口,P2 的输出缓冲级可驱动(吸收或输出电流)4 个TTL 逻辑门电路。对端口写“1”,通过内部的上拉电阻把端口拉到高电平,此时可作输入口。作为输入口使用时,因为内部存在上拉电阻,某个引脚被外部信号拉低时会输出一个电流(IIL)。在访问外部程序存储器或16 位四肢的外部数据存储器(例如执行MOVX @DPTR指令)时,P2 口送出高8 位地址数据,在访问8 位地址的外部数据存储器(例如执行MOVX @ RI 指令)时,P2 口线上的内容(也即特殊功能寄存器(SFR)区中R2 寄存器的内容),在整个访问期间不改变。Flash 编程和程序校验时,P2 也接收高位地址和其他控制信号。

·P3 口:P3 是一个带有内部上拉电阻的8 位双向I/O 口,P3 的输出缓冲级可驱动(吸收或输出电流)4 个TTL 逻辑门电路。对端口写“1”,通过内部的上拉电阻把端口拉到高电平,此时可作输入口。作为输入口使用时,因为内部存在上拉电阻,某个引脚被外部信号拉低时会输出一个电流(IIL)。P3 口还接收一些用于Flash 闪速存储器编程和程序校验的控制信号。

·RST:复位输入。当振荡器工作时,RST 引脚出现两个机器周期以上高电平将使单片机复位。

·ALE/PROG:当访问外部程序存储器或数据存储器时,ALE(地址锁存允许)输出脉冲用于锁存地址的低8 位字节。即使不访问外部存储器,ALE 仍以时钟振荡频率的1/6 输出固定的正脉冲信号,因此它可对外输出时钟或用于定时目的。要注意的是,每当访问外部数据存储器时将跳过一个ALE 脉冲。对Flash 存储器编程期间,该引脚还用于输入编程脉冲(PROG)。如有必要,可通过对特殊功能寄存器(SFR)区中的8EH 单元D0 位置位,可禁止ALE 操作。该位置位后,只有一条MOVX 和MOVC 指令ALE 才会被激活。此外,该引脚会被微弱拉高,单片机执行外部程序时,应设置ALE 无效。

·PSEN:程序存储允许输出是外部程序存储器的读选通型号,当89C51 由外部存储器取指令(或数据)时,每个机器周期两次PSEN 有效,即输出两个脉冲。在此期间,当访问外部数据存储器,这两次有效的PSEN 信号不出现。

·EA/VPP:外部访问允许。欲使CPU 仅访问外部程序存储器(地址为0000H—FFFFH),EA 端必须保持低电平(接地)。需注意的是:如果加密位LB1 被编程,复位时内部会锁存EA 端状态。如EA 端为高电平(接Vcc 端),CPU 则执行内部程序存储器中的指令。Flash 存储器编程时,该引脚加上+12v 的编程允许电源Vpp,当然这必须是该器件使用12v 编程电压Vpp。

·XTAL1:振荡器反相放大器及内部时钟发生器的输入端。

·XTAL2:振荡器反相放大器的输出端。89C51 中有一个用于构成内部振荡器的高增益反相放大器,引脚XTAL1 和XTAL2分别是该放大器的输入端和输出端。这个放

大器与作为反馈元件的片外石英晶体或陶瓷谐振器一起构成自激振荡器,振荡电路参见图5。外接石英晶体或陶瓷谐振器及电容C1、C2 接在放大器的反馈回路中构成并联振荡电路。对电容C1、C2 虽没有十分严格的要求,但电容容量的大小会轻微影响振荡频率的高低、振荡器工作的稳定性、起振的难易程度及温度稳定性,如果使用石英晶体,我们推荐电容使用30Pf±10 Pf,而如使用陶瓷谐振器建议选择40Pf±10Pf。用户也可以采用外部时钟。这种情况下,外部时钟脉冲接到XTAL1 端,即内部时钟发生器的输入端XTAL2 则悬空。

掉电模式:

在掉电模式下,振荡器停止工作,进入掉电模式的指令是最后一条被执行的指令,片内RAM 和特殊功能寄存器的内容在终止掉电模式前被冻结。推出掉电模式的唯一方法是硬件复位,复位后将重新定义全部特殊功能寄存器但不改变RAM 中的内容,在Vcc 恢复到正常工作电平前,复位应无效,且必须保持一定时间以使振荡器重启动并稳定工作。89C51 的程序存储器阵列是采用字节写入方式编程的,每次写入一个字符,要对整个芯片的EPROM 程序存储器写入一个非空字节,必须使用片擦除的方法将整个存储器的内容清楚。

5 AT89C52单片机介绍

AT89C52是美国Atmel公司生产的低电压、高性能CMOS 8位单片机,片内含8KB 的可反复擦写的程序存储器和12B的随机存取数据存储器(RAM),器件采用Atmel 公司的高密度、非易失性存储技术生产,兼容标准MCS-51指令系统,片内配置通用8位中央处理器(CPU)和Flash存储单元,功能强大的AT89C52单片机可灵活应用于各种控制领域。AT89C52单片机属于AT89C51单片机的增强型,与Intel公司的80C52在引脚排列、硬件组成、工作特点和指令系统等方面兼容。

其主要工作特性是:

片内程序存储器内含8KB的Flash程序存储器,可擦写寿命为1000次;

片内数据存储器内含256字节内部RAM;

具有32根可编程I/O口线;

具有3个可编程定时器;

2个可编程I/O口线;

中断系统具有8个中断源;

串行口是具有一个全双工的可编程串行通信口;

低功耗工作模式有空闲模式和掉电模式;

具有可编程的3级程序锁定位;

AT89C52最高工作频率为24MHz。

功能特性描述:

AT89C52是一种低功耗、高性能CMOS8位微控制器,具有8K在系统可编程Flash存储器,使用Atmel公司的高密度、非易失性存储技术制造,与工业80C51产品指令和引脚完全兼容。片上Flash允许程序存储器在系统可编程,亦适用于常规编程器。在单芯片上,拥有灵巧的8位CPU和在系统可编程Flash,使得AT89C52为众多嵌入式控制应用系统提供高灵活、超有效的解决方案。

AT89C52具有以下标准功能:

8k字节Flash,256字节RAM,32位I/O口线,看门狗定时器,2个数据指针,三个16位定时/计数器,一个6向量2级中断结构,全双工串行口,片内晶振及时钟电路。另外,AT89C52可降至0Hz静态逻辑操作,支持2种软件可选择节电模式。空闲模式下,CPU停止工作,允许RAM、定时/计数器、串口、中断继续工作。掉电保护方式下,RAM 内容被保存,振荡器被冻结,单片机一切工作停止,知道下一个中断或硬件复位为止。8位微控制器、8K字节在系统可编程。

AT89C52有40个引脚,32个外部双向输入/输出(I/O)端口,同时内含2个外中端口,3个16位可编程定时计数器,2个全双工串行通信口,2个读写口线,AT89C52可以按照常规方法进行编程,也可以在线编程。其将通用的微处理器和Flash存储器结合在一起,特别是可反复擦写的Flash存储器可有效的降低开发成本。

6 编程方法

编程前,设置好地址、数据及控制信号,编程单元的地址加在P1 口和P2 口的P2.0—P2.3(11 位地址范围为0000H——0FFFH),数据从P0口输入,引脚P2.6、P2.7 和P3.6、P3.7 的电平设置见表6,PSEB 为低电平,RST保持高电平,EA/Vpp 引脚是编程电源的输入端,按要求加上编程电压,ALE/PROG引脚输入编程脉冲(负脉冲)。编程时,可采用4—20MHz 的时钟振荡器,89C51 编程方法如下:在地址线上加上要编程单元的地址信号在数据线上加上要写入的数据字节。激活相应的控制信号。在高电压编程方式时,将EA/Vpp 端加上+12v 编程电压。每对Flash 存储阵列写入一个字节或每写入一个程序加密位,加上一个ALE/PROG 编程脉冲。改变编程单元的地址和写入的数据,重复1—5 步骤,知道全部文件编程结束。每个字节写入周期是自身定时的,通常约为1.5ms。·数据查询89C51 单片机用数据查询方式来检测一个写周期是否结束,在一个写周期中,如需要读取最后写入的那个字节,则读出的数据的最高位(P0.7)是原来写入字节的最高位的反码。写周期开始后,可在任意时刻进行数据查询。

6.1Ready/Busy:

字节编程的进度可通过Ready/Busy 输出信号检测,编程期间,ALE 变为高电平“H”后P3.4(Ready/Busy)端被拉低,表示正在编程状态(忙状态)。编程完成后,P3.4 变为高电平表示准备就绪状态。

·程序校验:如果加密位LB、LB2 没有进行编程,则代码数据可通过地址和数据线读回原编写的数据,采用下图的电路,程序存储器的地址由P1 口和P2 口的P2.0—P2.3 输入,数据由P0 口读出,P206、P2.7 和P3.6、P3.7 的控制信号见表6,PSEN 保持低电平,ALE、EA 和RST 保持高电平。校验时,P0 口必须接上10k 左右的上拉电阻。

6.2芯片擦除:

利用控制信号的正确组合(表6)并保持ALE/PROG 引脚10ms 的低电平脉冲宽度即可将EPROM 阵列(4k 字节)和三个加密位整片擦除,代码阵列在片擦除操作中将任何非空单元写入”1”,这步骤需在编程之前进行。

6.3读片内签名字节:

89C51 单片机内有3 个签名字节,地址为030H、031H 和032H。于声明该器件的厂商、号和编程电压。读签名字节的过程和单元030H、031H 和032H的正常校验相仿,只需要将P3.6 和P3.7 保持低电平,返回值意义如下:

(030H) = 1EH 声明产品由ATMEL 公司制造。

(031H) = 51H 声明为89C51 单片机。

(032H) = FFH 声明为12V 编程电压。

(032H) = 05H 声明为5 编程电压。

6.4 编程接口:

采用控制信号的正确组合可对Flash 闪速存储阵列中的每一代码字节进行写入和存储器的整片擦除,写操作周期是自身定时的,初始化后它将自动定时到操作完成。微机接口实现两种信息形式的交换。在计算机之外,由电子系统所处理的信息以一种物理信号形式存在,但在程序中,它是用数字表示的。任一接口的功能都可分为以某种形式进行数据库变换的一些操作,所以外部和内部形式的转换是由许多步骤完成的。模拟-数字转换器(ADC)用来将连续变化信号变成相应的数字量,这数字量可是可能性的二进制数值中的一固定值。如果传感器输出不是连续变化的,就不需模拟-数字转换。这种情况下,信号调理单元必须将输入信号变换成为另一信号,也可直接与接口的下一部分,即微计算机本身的输入输出单元相连接。输出接口采用相似的形式,明显的差别在于信息流的方向相反;是从程序到外部世界。这种情况下,程序可称为输出程序,它监督接口的操作并完成数字-模拟转换器(DAC)所需数字的标定。该子程序依次送出信息给输出器件,产生相应的电信号,由DAC 转换成模拟形式。最后,信号经调理(通常是放大)以形成适应于执行器操作的形式。在微机电路中使用的信号几乎总是太小而不能被直接地连到“外部世界”,因而必须用某种形式将其转换成更适宜的形式。接口电路部分的设计是使用微机的工程师所面临最重要的任务之一。我们已经了解到微机中,信号以离散的位形式表示。当微机要与只有打开或关闭

操作的设备相连时,这种数字形式是最有用的,这里每一位都可表示一开关或执行器的状态。为了解决实际问题,一个单片机不仅包括CPU,程序和数据存储器,另外,它必须含有通过CPU 访问外部信息的硬件。一旦CPU 收集到数据信息和流程,它必须能够改变外部领域的一部分,这些硬件设备称作外围设备,它们是CPU 通往外部的窗口。

单片机可利用外围设备中最基本的用于一般用途的I/O 接口,每个I/O 接口既可作为输入端又可作为输出端,每个I/O 接口的功能取决与程序初始化阶段对数据方位寄存器相应位进行置一和清零操作,通过CPU 指令对数据寄存器相应位进行置一和清零来置一和清零输出端口,同样输入端口逻辑位也可以通过CPU 指令访问。一些类型的串行口单元允许CPU 与外部设备进行串口通信,用串口位代替平行位进行通信需要少许的I/O 口,这样使通信费用降低但速度也相对慢些。串口传送可以同步也可以异步。

MCU

1 The definition of MCU

Also known as single-chip MCU(Microcontroller),because it was first used in the field of industrial control.Only by the single-chip CPU chip developed from the dedicated processor.The design concept is the first by a large number of peripherals and CPU in a single chip,the computer system so that smaller,more easily integrated into the complex and demanding on the volume control devices.INTEL the Z80 is one of the first design in accordance with the idea of the processor,From then on,the MCU and the development of a dedicated processor parted ways.

Early MCU 8-bit or all of the four. One of the most successful is the INTEL 8031, because the performance of a simple and reliable access to a lot of good praise. Then developed in 8031 out of MCS51 MCU Systems. SCM systems based on this system until now is still widely used. With the increased requirements of industrial control field, began a 16-bit microcontroller, because the cost is not satisfactory but have not been very widely used. After 90 years with the great development of consumer electronics, microcontroller technology has been a huge increase. With INTEL i960 series, especially the later series of widely used ARM, 32-bit microcontroller quickly replace high-end 16-bit MCU status and enter the mainstream market. The traditional 8-bit microcontroller performance have been the rapid increase capacity increase compared to 80 the number of times. Currently, high-end 32-bit microcontroller clocked over 300MHz, the performance catching the mid-90's dedicated processor, while the average model prices fall to one U.S. dollars, the most high-end [1] model only 10 dollars.Modern SCM systems are no longer only in the development and use of bare metal environment, a large number of proprietary embedded operating system is widely used in the full range of SCM. The handheld computers and cell phones as the core processing of high-end microcontroller can even use a dedicated Windows and Linux operating systems.

More than a dedicated MCU processor suitable for embedded systems, so it was up to the application. In fact the number of SCM is the world's largest computer. Modern human life used in almost every piece of electronic and mechanical products will be integrated single chip.Phone, telephone, calculator, home appliances, electronic toys, handheld computers and computer accessories such as a mouse with a 1-2 in both the Department of SCM. Personal computer will have a large number of SCM in the work. General car with more than 40 SCM, complex industrial control systems may even have hundreds of SCM

in the same time work! SCM is not only far exceeds the number of PC and other computing the sum, or even more than the number of human beings.

2 MCU history

Single-chip 70 was born in the late 20th century, experienced a SCM, MCU, SOC three stages.

(1)SCM the single chip microcomputer (Single Chip Microcomputer) stage, mainly seeking the best of the best single form of embedded systems architecture. "Innovation model" success, laying the SCM and general computer completely different path of development. In the open road of independent development of embedded systems, Intel Corporation contributed.

(2)MCU the micro-controller (Micro Controller Unit) stage, the main direction of technology development: expanding to meet the embedded applications, the target system requirements for the various peripheral circuits and interface circuits, highlight the object of intelligent control.It involves the areas associated with the object system, therefore, the development of MCU's responsibility inevitably falls on electrical, electronics manufacturers. From this point of view, Intel faded MCU development has its objective factors. In the development of MCU, the most famous manufacturers as the number of Philips Corporation.

Philips company in embedded applications, its great advantage, the MCS-51 single-chip micro-computer from the rapid development of the micro-controller. Therefore, when we look back at the path of development of embedded systems, do not forget Intel and Philips in History. (3)Embedded system microcontroller is an independent development path, the MCU important factor in the development stage, is seeking applications to maximize the solution on the chip; Therefore, the development of dedicated single chip SOC trend of the natural form. As the microelectronics, IC design, EDA tools development, application system based on MCU SOC design have greater development. Therefore, the understanding of the microcontroller chip microcomputer can be, extended to the single-chip micro-controller applications.

3 MCU applications

At present,MCU to infiltrate all areas of our lives, which is almost difficult to find traces of the field without SCM. Missile navigation equipment, aircraft, all types of instrument control, computer network communications and data transmission, industrial automation, real-time process control and data processing, extensive use of various smart IC card, civilian luxury car security system, video recorder, camera, fully automatic

washing machine control, and program-controlled toys, electronic pet, etc., which are inseparable from the microcontroller. Not to mention the area of robot control, intelligent instruments, medical equipment was. Therefore, the MCU learning, development and application of the large number of computer applications and intelligent control of the scientists, engineers.

SCM is widely used in instruments and meters, household appliances, medical equipment, aerospace, specialized equipment, intelligent management and process control fields, roughly divided into the following several areas:

(1)In the application of Intelligent Instruments

SCM has a small size, low power consumption, controlling function, expansion flexibility, the advantages of miniaturization and ease of use, widely used instrument, combining different types of sensors can be realized Zhuru voltage, power, frequency, humidity, temperature, flow, speed, thickness, angle, length, hardness, elemental, physical pressure measurement. SCM makes use of digital instruments, intelligence, miniaturization, and functionality than electronic or digital circuits more powerful. Such as precision measuring equipment (power meter, oscilloscope, various analytical instrument).

(2)In the industrial control application

With the MCU can constitute a variety of control systems, data acquisition system. Such as factory assembly line of intelligent control,all kinds of alarm systems,and computer networks constitute a secondary control system.

(3)In the Appliance of Household appliances

It can be said that the appliances are basically using SCM, praise from the electric rice, washing machines, refrigerators, air conditioners, color TV, and other audio video equipment, to the electronic weighing equipment, varied, and omnipresent.

(4)In the field of computer networks and communications applications

MCU general with modern communication interface, can be easy with the computer data communication, networking and communications in computer applications between devices had excellent material conditions, are basically all communication equipment to achieve a controlled by MCU from mobile phone, telephone, mini-program-controlled switchboards, building automated communications call system, train radio communication, to the daily work can be seen everywhere in the mobile phones, trunked mobile radio, walkie-talkies, etc..

(5)Microcomputer in the field of medical device applications

MCU in the use of medical devices is also quite extensive, such as medical respirator, the various analyzers, monitors, ultrasound diagnostic equipment and hospital beds, etc. call system.

(6)In a variety of major appliances in the modular applications

Designed to achieve some special single specific function to be modular in a variety of circuit applications, without requiring the use of personnel to understand its internal structure. If music integrated single chip, seemingly simple function, miniature electronic chip in the net (the principle is different from the tape machine), you need a computer similar to the principle of the complex. Such as: music signal to digital form stored in memory (like ROM), read by the microcontroller, analog music into electrical signals (similar to the sound card).

In large circuits, modular applications that greatly reduce the volume, simplifies the circuit and reduce the damage, error rate, but also easy to replace.

(7)Microcontroller in the application field of automotive equipment

SCM in automotive electronics is widely used, such as a vehicle engine controller, CAN bus-based Intelligent Electronic Control Engine, GPS navigation system, abs anti-lock braking system, brake system, etc..

In addition, the MCU in business, finance, research, education, national defense, aerospace and other fields has a very wide range of applications.

4 MCU introduced

MCU ,also known as single-chip microcontroller, it is not complete a certain logic chips, but to a computer system integrated into a chip.Equivalent to a micro-computer, and computer than just the lack of a microcontroller I / O devices. General talk: a chip becomes a computer. Its small size, light weight, cheap, for the study, application and development of facilities provided. At the same time, learning to use the MCU is to understand the principle and structure of the computer the best choice.

MCU and the computer use is also similar to the module, such as CPU, memory, parallel bus, as well as the role and the same hard disk memory,is it different from the performance of these components are relatively weak in our home computer a lot ,but the price is low , there is generally no more than 10 yuan ......can use it to make some control for a class of electrical work is not very complex is sufficient.We are using automatic drum washing machines ,smoke hood, VCD and so on inside the home appliances can see it's shadow!......It is mainly as part of the core component of the control.

It is an online real-time control computer, control-line is that the scene is needed is a stronger anti-jamming ability, low cost, and this is, and off-line computer (such as home PC), the main difference.

By single-chip process ,and can be amended.Through different procedures to achieve different functions, in particular special unique features, this is another device much effort

needs to be done, some great efforts are very difficult to do. A not very complex functions if the 50's with the United States developed 74 series, or the 60's CD4000 series of these pure hardware buttoned, then the circuit must be a large PCB board! But if the United States if the 70's with a series of successful SCM market, the result will be a drastic change! Just because you are prepared by microcomputer programs can achieve high intelligence, high efficiency and high reliability!

MCU and the computer use is also similar to the module, such as CPU, memory, parallel bus, as well as the role and the same hard disk memory,is it different from the performance of these components are relatively weak in our home computer a lot ,but the price is low , there is generally no more than 10 yuan ......can use it to make some control for a class of electrical work is not very complex is sufficient.We are using automatic drum washing machines ,smoke hood, VCD and so on inside the home appliances can see it's shadow!......It is mainly as part of the core component of the control.

It is an online real-time control computer, control-line is that the scene is needed is a stronger anti-jamming ability, low cost, and this is, and off-line computer (such as home PC), the main difference.

By single-chip process ,and can be amended.Through different procedures to achieve different functions, in particular special unique features, this is another device much effort needs to be done, some great efforts are very difficult to do. A not very complex functions if the 50's with the United States developed 74 series, or the 60's CD4000 series of these pure hardware buttoned, then the circuit must be a large PCB board! But if the United States if the 70's with a series of successful SCM market, the result will be a drastic change! Just because you are prepared by microcomputer programs can achieve high intelligence, high efficiency and high reliability!

As the microcontroller on the cost-sensitive, so now the dominant software or the lowest level assembly language, which is the lowest level in addition to more than binary machine code language, and as so low why is the use? Many high-level language has reached the level of visual programming Why is not it? The reason is simply that there is no home computer as a single chip CPU, not as hard as a mass storage device.A visualization of small high-level language program which even if only one button, will reach tens of K of size! For the home PC's hard drive in terms of nothing, but in terms of the MCU is not acceptable. SCM in the utilization of hardware resources to be very high for the job so although the original is still in the compilation of a lot of use. The same token, if the giant computer operating system and applications run up to get home PC, home PC, also can not afford to.

Can be said that the twentieth century across the three "power" era, that is, the age of

electricity, the electronic age and has entered into the computer age. However, this computer, usually refers to the personal computer, referred to as PC. It consists of the host, keyboard, monitor and other components. Another type of computer, most people do not know how. This computer is to give all kinds of intelligent machines single chip (also known as micro-controller). As the name suggests, this computer system took only a minimal integrated circuit, can be a simple operation and control. Because it is small, usually hidden in the charged mechanical "stomach" in. It is in the device, like the human brain plays a role, it goes wrong, the whole plant was paralyzed. Now, this microcontroller has a very broad field of use, such as smart meters, real-time industrial control, communications equipment, navigation systems, and household appliances. Once all kinds of products were using SCM, can serve to upgrade the effectiveness of products, often in the product name preceded by the adjective - "intelligent," such as intelligent washing machines. Now some technical personnel of factories or other amateur electronics developers to engage in out of certain products, not the circuit is too complicated, that function is too simple and can easily be copied. The reason may be stuck in the product did not use a microcontroller or other programmable logic device.

4.1 AT89C51Introduction

The 8-bit AT89C51 CHMOS microcontrollers are designed to handle high-speed calculations and fast input/output operations. MCS 51 microcontrollers are typically used for high-speed event control systems. Commercial applications include modems, motor-control systems, printers, photocopiers, air conditioner control systems, disk drives, and medical instruments. The automotive industry use MCS 51 microcontrollers in engine-control systems, airbags, suspension systems, and antilock braking systems (ABS). The AT89C51 is especially well suited to applications that benefit from its processing speed and enhanced on-chip peripheral functions set, such as automotive power-train control, vehicle dynamic suspension, antilock braking, and stability control applications. Because of these critical applications, the market requires a reliable cost-effective controller with a low interrupt latency response, ability to service the high number of time and event driven integrated peripherals needed in real time applications, and a CPU with above average processing power in a single package. The financial and legal risk of having devices that operate unpredictably is very high. Once in the market, particularly in mission critical applications such as an autopilot or anti-lock braking system, mistakes are financially prohibitive. Redesign costs can run as high as a $500K, much more if the fix means 2 back annotating it across a product family that share the same core and/or peripheral design flaw. In addition, field replacements of components is extremely

expensive, as the devices are typically sealed in modules with a total value several times that of the component. To mitigate these problems, it is essential that comprehensive testing of the controllers be carried out at both the component level and system level under worst case environmental and voltage conditions. This complete and thorough validation necessitates not only a well-defined process but also a proper environment and tools to facilitate and execute the mission successfully. Intel Chandler Platform Engineering group provides post silicon system validation (SV) of various micro-controllers and processors. The system validation process can be broken into three major parts. The type of the device and its application requirements determine which types of testing are performed on the device.

4.2 The AT89C51 provides the following standard features:

4Kbytes of Flash, 128 bytes of RAM, 32 I/O lines, two 16-bittimer/counters, a five vector two-level interrupt architecture, a full duple serial port, on-chip oscillator and clock circuitry. In addition, the AT89C51 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port and interrupt sys -tem to continue functioning. The Power-down Mode saves the RAM contents but freezes the oscillator disabling all other chip functions until the next hardware reset.

4.3 Pin Description

VCC Supply voltage.

GND Ground.

Port 0:Port 0 is an 8-bit open-drain bi-directional I/O port. As an output port, each pin can sink eight TTL inputs. When 1s are written to port 0 pins, the pins can be used as high impedance inputs .Port 0 may also be configured to be the multiplexed low order address/data bus during accesses to external program and data memory. In this mode P0 has internal pullups. Port 0 also receives the code bytes during Flash programming, and outputs the code bytes during program verification. External pullups are required during program verification.

Port 1:Port 1 is an 8-bit bi-directional I/O port with internal pullups. The Port 1 output buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins they are pulled high by the internal pullups and can be used as inputs. As inputs, Port 1 pins that are externally being pulled low will source current (IIL) because of the internal pullups. Port 1 also receives the low-order address bytes during Flash programming and verification.

Port 2:Port 2 is an 8-bit bi-directional I/O port with internal pullups. The Port 2

output buffers can sink/source four TTL inputs. When 1s are written to Port 2 pins they are pulled high by the internal pullups and can be used as inputs. As inputs, Port 2 pins that are externally being pulled low will source current (IIL) because of the internal pullups. Port 2 emits the high-order address byte during fetches from external program memory and during accesses to Port 2 pins that are externally being pulled low will source current (IIL) because of the internal pullups. Port 2 emits the high-order address byte during fetches from external program memory and during accesses to external data memory that use 16-bit addresses (MOVX@DPTR). In this application, it uses strong internal pull-ups when emitting 1s. During accesses to external data memory that use 8-bit addresses (MOVX @ RI), Port 2 emits the contents of the P2 Special Function Register. Port 2 also receives the high-order address bits and some control signals during Flash programming and verification.

Port 3:Port 3 is an 8-bit bi-directional I/O port with internal pull ups. The Port 3 output buffers can sink/source four TTL inputs. When 1s are written to Port 3 pins they are pulled high by the internal pullups and can be used as inputs. As inputs, Port 3 pins that are externally being pulled low will source current (IIL) because of the pullups.

Port 3 also serves the functions of various special feature soft the AT89C51 as listed below:

RST:Reset input. A high on this pin for two machine cycles while the oscillator is running resets the device.

ALE/PROG:Address Latch Enable output pulse for latching the low byte of the address during accesses to external memory. This pin is also the program pulse input (PROG) during Flash programming. In normal operation ALE is emitted at a constant rate of 1/6 the oscillator frequency, and may be used for external timing or clocking purposes. Note, however, that one ALE pulse is skipped during each access to external Data Memory. If desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the bit set, ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is weakly pulled high. Setting the ALE-disable bit has no effect if the microcontroller is in external execution mode.

PSEN:Program Store Enable is the read strobe to external program memory. When theAT89C51 is executing code from external program memory, PSEN is activated twice each machine cycle, except that two PSEN activations are skipped during each access to external data memory.

EA/VPP:External Access Enable. EA must be strapped to GND in order to enable the device to fetch code from external program memory locations starting at 0000H up to FFFFH. Note, however, that if lock bit 1 is programmed, EA will be internally latched on

reset. EA should be strapped to VCC for internal program executions. This pin all receives the 12-volt programming enable voltage (VPP) during Flash programming, for parts that require 12-volt VPP.

XTAL1:Input to the inverting oscillator amplifier and input to the internal clock operating circuit.

XTAL2:Output from the inverting oscillator amplifier. Oscillator CharacteristicsXTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier which can be configured for use as an on-chip oscillator, as shown in Figure 1. Either a quarts crystal or ceramic resonator may be used. To drive the device from an external clock source, XTAL2 should be left unconnected while XTAL1 is driven as shown in Figure 2.There are no requirements on the duty cycle of the external clock signal, since the input to the internal clocking circuitry is through a divide-by-two flip-flop, but minimum and maximum voltage high and low time specifications must be observed. Idle Mode In idle mode, the CPU puts itself to sleep while all the on chip peripherals remain active. The mode is invoked by software. The content of the on-chip RAM and all the special functions registers remain unchanged during this mode. The idle mode can be terminated by any enabled interrupt or by a hardware reset. It should be noted that when idle is terminated by a hard ware reset, the device normally resumes program execution, from where it left off, up to two machine cycles before the internal reset algorithm takes control. On-chip hardware inhibits access to internal RAM in this event, but access to the port pins is not inhibited. To eliminate the possibility of an unexpected write to a port pin when Idle is terminated by reset, the instruction following the one that invokes Idle should not be one that writes to a port pin or to external memory.

Power-down Mode

In the power-down mode, the oscillator is stopped, and the instruction that invokes power-down is the last instruction executed. The on-chip RAM and Special Function Registers retain their values until the power-down mode is terminated. The only exit from power-down is a hardware reset. Reset redefines the SFR but does not change the on-chip RAM. The reset should not be activated before VCC is restored to its normal operating level and must be held active long enough to allow the oscillator to restart and stabilize. The AT89C51 code memory array is programmed byte-by byte in either programming mode. To program any nonblank byte in the on-chip Flash Memory, the entire memory must be erased using the Chip Erase Mode.

5 AT89C52 chip explains

The AT89C52 is a low-power,high-performance CMOS 8-bit microcomputer with 8 K

bytes of Flash programmable and erasable read only memory(PEROM).The device is manufactured using Atmel's high density nonvolatile memory technology and is compatible with the industry standard 80C51 and 80C52 instruction set and pinot.The on-chip Flash allows the program memory to be reprogrammed in-system or by a conbventional onwolatile memory programmer.By combining a versatile 8-bit CPU with Flash on a monolithic chip,the Atmel AT89C52 is a powerful microcomputer,which provides a highly flexible and cost effective solution to many embedded control applications.

Eatures:

8 K bytes of In-system Reprogrammable Flash Memory;Endurance:1000 Write/Erase Cycles

256×8 bit Internal RAM

32 Programmable I/O Lines

Three 16-Bit Timer/Counters

Eight Interrupt Sources

Programmable Serial Channel

Low Power Idle and Power Down Modes

Three-Level Program Memory Lock

Fully Static Operation:0 Hz to 24 MHz

Description

The AT89C52 is a low-power,high-performance COMS 8-bit microcomputer

with 8K bytes of Flash programmable and erasable read only memory(PEROM).The device is manufactured using Atmel's high density nonvolatile memory technology and is compatible with the industry standard 80C51 and 80C52 instruction set and pinot.The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional onvolatile memory programmer.By combining a versatile 8-bit CPU with Flash on a monolithic chip,the Atmel AT89C52 is a powerful microcomputer,which provides a highly flexible and cost effective solution to many embedded control applications

The AT89C52 provides the following standard features:

8k bytes of Flash ,256 bytes of RAM,32 I/O lines,three 16-bit timer/counters,a six-vector two-level interrupt architecture , a full duplex serial port,on-chip oscillator,and clock circuitry . In addition, the AT89C52 is designed with static logic of operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM,timer/counter,serial port,and interrupt system to continue functioning. The Power Down Mode saves the RAM contents but

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外文资料原文 Software Development Concepts and Design Methodologies During the 1960s, ma inframes and higher level programming languages were applied to man y problems including human resource s yste ms,reservation s yste ms, and manufacturing s yste ms. Computers and software were seen as the cure all for man y bu siness issues were some times applied blindly. S yste ms sometimes failed to solve the problem for which the y were designed for man y reasons including: ?Inability to sufficiently understand complex problems ?Not sufficiently taking into account end-u ser needs, the organizational environ ment, and performance tradeoffs ?Inability to accurately estimate development time and operational costs ?Lack of framework for consistent and regular customer communications At this time, the concept of structured programming, top-down design, stepwise refinement,and modularity e merged. Structured programming is still the most dominant approach to software engineering and is still evo lving. These failures led to the concept of "software engineering" based upon the idea that an engineering-like discipl ine could be applied to software design and develop ment. Software design is a process where the software designer applies techniques and principles to produce a conceptual model that de scribes and defines a solution to a problem. In the beginning, this des ign process has not been well structured and the model does not alwa ys accurately represent the problem of software development. However,design methodologies have been evolving to accommo date changes in technolog y coupled with our increased understanding of development processes. Whereas early desig n methods addressed specific aspects of the

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外文文献: Knowledge of the stepper motor What is a stepper motor: Stepper motor is a kind of electrical pulses into angular displacement of the implementing agency. Popular little lesson: When the driver receives a step pulse signal, it will drive a stepper motor to set the direction of rotation at a fixed angle (and the step angle). You can control the number of pulses to control the angular displacement, so as to achieve accurate positioning purposes; the same time you can control the pulse frequency to control the motor rotation speed and acceleration, to achieve speed control purposes. What kinds of stepper motor sub-: In three stepper motors: permanent magnet (PM), reactive (VR) and hybrid (HB) permanent magnet stepper usually two-phase, torque, and smaller, step angle of 7.5 degrees or the general 15 degrees; reaction step is generally three-phase, can achieve high torque output, step angle of 1.5 degrees is generally, but the noise and vibration are large. 80 countries in Europe and America have been eliminated; hybrid stepper is a mix of permanent magnet and reactive advantages. It consists of two phases and the five-phase: two-phase step angle of 1.8 degrees while the general five-phase step angle of 0.72 degrees generally. The most widely used Stepper Motor. What is to keep the torque (HOLDING TORQUE) How much precision stepper motor? Whether the cumulative: The general accuracy of the stepper motor step angle of 3-5%, and not cumulative.

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Section 3 Design philosophy, design method and earth pressures 3.1 Design philosophy 3.1.1 General The design of earth retaining structures requires consideration of the interaction between the ground and the structure. It requires the performance of two sets of calculations: 1)a set of equilibrium calculations to determine the overall proportions and the geometry of the structure necessary to achieve equilibrium under the relevant earth pressures and forces; 2)structural design calculations to determine the size and properties of thestructural sections necessary to resist the bending moments and shear forces determined from the equilibrium calculations. Both sets of calculations are carried out for specific design situations (see 3.2.2) in accordance with the principles of limit state design. The selected design situations should be sufficiently Severe and varied so as to encompass all reasonable conditions which can be foreseen during the period of construction and the life of the retaining wall. 3.1.2 Limit state design This code of practice adopts the philosophy of limit state design. This philosophy does not impose upon the designer any special requirements as to the manner in which the safety and stability of the retaining wall may be achieved, whether by overall factors of safety, or partial factors of safety, or by other measures. Limit states (see 1.3.13) are classified into: a) ultimate limit states (see 3.1.3); b) serviceability limit states (see 3.1.4). Typical ultimate limit states are depicted in figure 3. Rupture states which are reached before collapse occurs are, for simplicity, also classified and

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