【正文】 儲器EEPROM。盡管圖中顯示的只有一個存儲單元，實際中有RAM和ROM兩種不同的存儲器被使用。存儲是利用存儲器電路，而的信息傳輸則是利用特定的輸入/輸出（I/O）電路。 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。 information is stored in a set of numbered ‘boxes’ and it is referenced by the serial number of the ‘box’ in question. Microputers use RAM Random Access Memory into which data can be written and from which data can be read again when needed. This data can be read back from the memory in any sequence desired, and not necessarily the same order in which it was written, hence the expression ‘random’ access memory. Another type of ROM Read Only Memory is used to hold fixed patterns of information which cannot be affected by the microprocessor。在系統(tǒng)中，處理是由系統(tǒng)完成的。外部的連接與工程系統(tǒng)的其余部分（即非計算機部分）有關(guān)。被廣泛使用的可編程ROM可利用特殊紫外線燈察除，并被成為EPROM，即可察除可編程只讀存儲器的縮寫。當(dāng)技術(shù)進(jìn)一步發(fā)展，更強更強的處理器和更大更大數(shù)量的存儲器被包含形成單片微型計算機，結(jié)果使最終產(chǎn)品的裝配成本得以節(jié)省。兩種情況下，序均能存于RAM，這讓程序能按應(yīng)用情況變化時進(jìn)行相應(yīng)的變化，但是這使得總系統(tǒng)易受掉電影響而工作不正常，除非使用電池保證供電連續(xù)性。水，是生活的必需品，也是在壓力之下提供給我們中的大多數(shù)人。這種系統(tǒng)常?？墒菤鈩踊蛘唠妱拥?。其標(biāo)準(zhǔn)范圍對電流來說是4～20mA DC，對電壓信號來說是1～5V DC?，F(xiàn)在盡管有許多其他類型的儀器在使用，這些填充式系統(tǒng)仍常用于直接的溫度測量。 功能特點 AT89S51內(nèi)提供了以下標(biāo)準(zhǔn)特性：4K字節(jié)閃存，128字節(jié)RAM，32個I / O線，兩個16位定時器/計數(shù)器，一個五向量兩級中斷結(jié)構(gòu)，一個全雙工串行口，片上振蕩器和時鐘電路。 進(jìn)修/編 地址鎖存使能鎖存在訪問外部存儲器地址的低字節(jié)