【正文】 he . products will be obsolete when the new standard for is introduced. Because of this, many PLC vendors are holding off on full MAP implementations. Omron, for example, has an ongoing MAPpatibility program。 but Frank Newburn, vice president of Omron39。s Industrial Division ,reports that because of the lack of a firm definition ,Omron39。s PLCs don39。t yet talk to MAP. Since it39。s unlikely that an individual PLC would talk to broad MAP anyway, makers are concentrating on proprietary works. According to Sal Provanzano, users fear that if they do get on board and vendors withdraw from MAP, they39。ll be the ones left holding a munications structure that39。s not supported. Universal I/O While there are concerns about the lack of patible munications between PLCs from different vendors, the connection at the other endthe I/Ois even more fragmented .With rare exceptions, I/O is still proprietary .Yet there are those who feel that I/O will eventually bee more universal .GE Fanuc is hoping to do that with its Genius smart I/O line. The independent I/O makers are pulling in the same direction. Many say that I/O is such a highvalue item that PLC makers will always want to keep it proprietary .As Ken Jannotta, says: The I/O is going to be a disproportionate amount of the hardware sale. Certainly each PLC vendor is going to try to protect that. For that reason, he says, PLC makers won39。t begin selling universal I/O system from other vendor. if we start selling that kind of product, says jannotta, what do we manufacture? With more intelligent I/O appearing, Sal Provanzano feels this will lead to more differentiation among I/O from different makers. Where the I/O bees extremely intelligent and bees part of the system, he says, it really is hard to define which is the I/O and which is CPU. It really CPU, if you will, is equally integrated into the system as the I/O. Connecting PLC I/O to PCs While different PLCs probably will continue to use proprietary I/O, several vendors make it possible to connect5 their I/O to IBM PCpatible equipment. Allebradeley, Could, and Cincinnati Milacron already have, and rumor has it that GE is planning something along these same lines .[4]Bill Ketelhut, manage of product planning at GE Fanuc North America ,sees this sort of thing as alternative to universal I/O.I think the trend ,instead of twoard universal I/O, will be multiple host interface , he says .Jodie Glore ,director of marking, Square D Automation Products, Views it as another indication that PLCs are, and have been for some time, industrial puters. 中文 譯文 單片機是電腦和集成電路發(fā)展的巔峰，有據(jù)可查的是他們也是 20 世紀最有意義的兩大發(fā)明。 一些廠家用 哈弗結構， 這種特性在硬件中 分離了 程序內存和數(shù)據(jù)內存，依據(jù)同樣的原理廣泛的適用于一般目的的電腦和微電腦 。 一些廠家 則采用 像 Princeton 結構， 不 劃分 程序內存和數(shù)據(jù)內存 。 這兩種特性在單片機中得到了充分的體現(xiàn)。 程 序 存 儲 器數(shù) 據(jù) 存 儲 器中 央 處 理 器 輸 入 / 輸 出 單 元 圖 A1 哈弗結構 數(shù) 據(jù) 存 儲 器 中 央 處 理 器 輸 入 / 輸 出 單 元 圖 A2 傳統(tǒng)的普林斯頓結構 只讀存貯器 (ROM) ROM 是通常的永久性的，非應用程序的易失性存儲器。 許多 微機和單片機用于大批量 的 應用，因此，要 經(jīng)濟 的 制造設備 就 要在制造期間的 把 程序存儲器 中 的內容永久性的刻錄在芯片中 。 這意味 著對 ROM 的開發(fā)是一種制約， ，因為制造之后 不能 修改 ROM 代碼。這一發(fā)展過程可能涉及仿真 ,使用硬件仿真功能以及強大的軟件工具使用先進的開發(fā)系統(tǒng)。 一些制造商在其提供的設備包括的范圍（或 專 用）用戶可編程內存 .其中最簡單的通常是設備能夠運行于微處理器模式通過使用一些輸入 /輸出作為地址線額外的 ROM 選項和數(shù)據(jù)總線訪問外部內存 。 這種類型的設備可以 表現(xiàn)為單芯片微型計算機盡管有限制的 I/O 和外部修改這些設備的電路 。 小內存裝置的應用在永久性內存的制造中是非常普遍的 ； 但 此 I/O 和其它芯片相比，基于微處理器的傳統(tǒng)電路仍然可以在我節(jié)省大量成 。 更 多更新?lián)Q代 的 ROM 設備，可在與形式 多樣的“ 背馱式 ” EPROM（可