【正文】 these patterns are not lost when power is removed and are normally used to hold the program which defines the behavior of a microprocessor based system. ROMs can be read like RAMs, but unlike RAMs they cannot be used to store variable information. Some ROMs have their data patterns put in during manufacture, while others are programmable by the user by means of special equipment and are called programmable ROMs. The widely used programmable ROMs are erasable by means of special ultraviolet lamps and are referred to as EPROMs, short for Erasable Programmable Read Only Memories. Other new types of device can be erased electrically without the need for ultraviolet light, which are called Electrically Erasable Programmable Read Only Memories, EEPROMs. The microprocessor processes data under the control of the program, controlling the flow of information to and from memory and input/output devices. Some input/output devices are generalpurpose types while others are designed for controlling special hardware such as disc drives or controlling information transmission to other puters. Most types of I/O devices are programmable to some extent, allowing different modes of operation, while some actually contain specialpurpose microprocessors to permit quite plex operations to be carried out without directly involving the main microprocessor. The microprocessor processes data under the control of the program, controlling the flow of information to and from memory and input/output devices. Some input/output devices are generalpurpose types while others are designed for controlling special hardware such as disc drives or controlling information transmission to other puters. Most types of I/O devices are programmable to some extent, allowing different modes of operation, while some actually contain specialpurpose microprocessors to permit quite plex operations to be carried out without directly involving the main microprocessor. The microprocessor , memory and input/output circuit may all be contained on the same integrated circuit provided that the application does not require too much program or data storage . This is usually the case in lowcost application such as the controllers used in microwave ovens and automatic washing machines . The use of single package allows considerable cost savings to e made when articles are manufactured in large quantities . As technology develops , more and more powerful processors and larger and larger amounts of memory are being incorporated into single chip microputers with resulting saving in assembly costs in the final products . For the foreseeable future , however , it will continue to be necessary to interconnect a number of integrated circuits to make a microputer whenever larger amounts of storage or input/output are required. Another major engineering application of microputers is in process control. Here the presence of the microputer is usually more apparent to the user because provision is normally made for programming the microputer for the particular application. In process control applications the benefits lf fitting the entire system on to single chip are usually outweighed by the high design cost involved, because this sort lf equipment is produced in smaller quantities. Moreover, process controllers are usually more plicated so that it is more difficult to make them as single integrated circuits. Two approaches are possible。 Microputer Systems Electronic systems are used for handing information in the most general sense。該反向放大器可以配置為片內(nèi)振蕩器。在 FLASH編程期間，此引腳也用于施加 12V編程電源（ VPP）。在由外部程序存儲器取指期間，每個機器周期兩次 /PSEN有效。此時， ALE只有在執(zhí)行MOVX， MOVC指令是 ALE才起作用。在平時， ALE端以不變的頻率周期輸出正脈沖信號，此頻率為振蕩器頻率的 1/6。否則，腳弱拉高。該引腳也是在 flash編程脈沖輸入 ALE（編）是在 1 / 6振蕩器頻率恒定 的速率發(fā)射，并可能對外部定時或時鐘的用途。作為輸入，由于外部下拉為低電平， P3口將輸出電流（ ILL）這是由于上拉的緣故。在給出地址“ 1”時，它利用內(nèi)部上拉優(yōu)勢，當對外部八位地址數(shù)據(jù)存儲器進行讀寫時， P2口輸出其特殊功能寄存器的內(nèi)容。 P2口： P2口為一個內(nèi)部上拉電阻的 8位雙向 I/O口， P2口緩沖器可接收，輸出 4個 TTL門電流，當 P2口被寫“ 1”時，其管腳被內(nèi)部上拉電阻拉高，且作為輸入。在 FIASH編程時， P0 口作為原碼輸入口，當 FIASH進行校驗時， P0輸出原碼，此時 P0外部必須被拉高。 接地：接地。此外， AT89C51是靜態(tài)邏輯設計與操作頻率下降到零，并支持兩種軟kPamAkPamAkPakPa mAmAKr 420 ????? 件可選的節(jié)電模式。該設備是采用 Atmel 的高密度非易失性內(nèi)存技術(shù)，并與行業(yè)標準的 MCS 51指令集和引腳兼容。有代表性的溫度傳感器包括：填充式熱系統(tǒng)、玻璃液體溫度計、熱電偶、電阻溫度探測器、熱敏電阻、雙金屬器件、光學和輻射高溫計和熱敏涂料。假定電子壓力傳感器的量程為 0～ 600kPa，增益定義為輸出變化除以輸入變化。當今，另一種電信號形式變的越來越常用，就是數(shù)字或離散信號。變送器輸出 —對氣動變送器是輸出壓力 —通過管道傳給記錄或控制儀表。使用這種系統(tǒng)，就可以在某一地點安裝大多數(shù)的指示、記錄和控制儀器。 在過程工廠中，將控制儀表遠遠放在過程的附近是不現(xiàn)實的，并且大多數(shù)測量是不容易從遠處傳來的。在典型的過程工廠中，壓力影響沸點溫度、凝固點溫度、過程效率、消耗和其他重要因數(shù)。而在本設計中壓力和壓力變送器當某一力加到某一面積上，就形成壓力，假如這力是 1牛頓均勻地加在 1平方米的面積上，這壓力被定義為 1帕斯卡。另一種選擇是將程序在 ROM中，這樣他們就變成電子 “硬件 ”的一部分并常被稱為 “固件 ”。而且，過程控制器通常更為復雜，所以要將他們做成單獨的集成電路就更為困難。但是在可預見的未來，當需要大量的存儲器或輸入 /輸出時，還是有必要繼續(xù)將許多集 成電路相互聯(lián)結(jié)起來，形成微計算機。 假如應用中不需要太多的程序和數(shù)據(jù)存儲量，微處理器、存儲器和輸入 /輸出可全被包含在同一集成電路中。另有新類型的期器件不必用紫外線燈而用電察除，所以稱為電可察除可編程只讀存儲器 EEPROM。另一類型 ROM（只讀存儲器） 是 用來保持 信息的，它們是 不受微處理器影響的固定的信息標本；這些 信息 在電源切斷后不會丟失，并通常用來保存規(guī)定微處理器化系統(tǒng)運轉(zhuǎn)過程的程序。 盡管圖中顯示的只有一個存儲單元， 但是在 實際中 卻 有 RAM和 ROM兩種不同的存儲器被使用。這種設計過程主要是軟件工程，而且在生產(chǎn)軟件時，就會遇到產(chǎn)生于常規(guī)工程中相