【正文】
假如應(yīng)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(biāo)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(shè)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)工程中相似的構(gòu)造和維護問題。存儲是利用存儲器電路,而從系統(tǒng)中輸入和輸出的信息傳輸則是利用特定的輸入/輸出(I/O)電路。現(xiàn)如今,以微處理器為基礎(chǔ)的系統(tǒng)從常規(guī)的處理方法中分離了出來,它將信息的處理,信息的存儲和信息的傳輸三個功能分離形成不同的系統(tǒng)單元。 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 , 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