【正文】 朱迪格洛爾，市場(chǎng)經(jīng)理，Square D Automation Products，將PLC看做是工業(yè)電腦。隨著分布式的發(fā)展，如果你愿意，CPU也同樣可以納入作為I/O的系統(tǒng)”。當(dāng)然每個(gè)PLC供應(yīng)商將試圖保護(hù)這一點(diǎn)。各個(gè)獨(dú)立I/O制造商都在同一方向進(jìn)發(fā)。通用的I / O然而大多數(shù)PLC的兼容問(wèn)題不同廠商的溝通不夠，在另一端連接的I/O問(wèn)題，更是支離破碎的。 例如Omron，擁有一個(gè)完整的兼容程序。拉里科馬雷克說(shuō)：“現(xiàn)在，規(guī)范仍然是一個(gè)移動(dòng)目標(biāo)，規(guī)范沒(méi)有最終決定，對(duì)于制造商?！盉ill Barkovitz， Triconex的總統(tǒng)，預(yù)言：“今后所有的控制器在過(guò)程控制系統(tǒng)的業(yè)務(wù)將引用更多的PLC技術(shù)， PLC功能比以往任何時(shí)候都要多?！爸唬彼f(shuō)，“是其中的過(guò)程控制系統(tǒng)，目前已被沒(méi)有理由自動(dòng)化DCS的大小[分布式控制系統(tǒng)]隨著價(jià)格標(biāo)簽開(kāi)始?！?Jannotta說(shuō)。舉例來(lái)說(shuō)，很難寫(xiě)三角函數(shù)使用梯形邏輯。許多時(shí)鐘電路，還具有電阻和低電容工作成本定時(shí)元件，也可以從外部源驅(qū)動(dòng)。有時(shí)候與定時(shí)器相關(guān)的是一個(gè)事件計(jì)數(shù)器。這種類(lèi)型的定時(shí)器通常在所要求的數(shù)量可重載中應(yīng)用。然后由硬件電路完成適當(dāng)格式的數(shù)據(jù)序列化處理。這種通訊也可被用來(lái)連接特殊功能的芯片和幾個(gè)微型機(jī)。有些I/O線適合直接連接到設(shè)備，例如，熒光顯示器，也可以提供足夠的電流，使接口和其他設(shè)備直接相連。這些線很容易和二進(jìn)制的設(shè)備相連接使用，如開(kāi)關(guān)，恒溫器，固態(tài)繼電器，閥門(mén)，電機(jī)等。中央處理單元（CPU）CPU 跟微處理器很相像。存儲(chǔ)依據(jù)設(shè)備的大小不同而類(lèi)型有所不同，但作為處理器具有相同的特征寬度（4,8,16 比特等）。更多更新?lián)Q代的ROM設(shè)備，可在與形式多樣的“背馱式” EPROM（可擦除可編程只讀存儲(chǔ)器）插座或存儲(chǔ)器相兼容，而不是ROM器件。這一發(fā)展過(guò)程可能涉及仿真,使用硬件仿真功能以及強(qiáng)大的軟件工具使用先進(jìn)的開(kāi)發(fā)系統(tǒng)。這兩種特性在單片機(jī)中得到了充分的體現(xiàn)。s not supported.Universal I/OWhile 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。s PLCs don39。ve heard a lot about MAP in the last few years ,and a lot of panies have jumped on the bandwagon. Many, however, were disappointed when a fullydefined and pleted MAP specification didn39。s increasing use such industries as food ,chemicals ,and petroleum. Ryan feels there are two types of applications in which they39。s very difficult to write a trigonometric function using ladder logic. Languages gaining acceptance include Boolean, control system flowcharting, and such function chart languages as Graphcet and its variation .And there39。 in most a mechanism is provided to at least allow some flexibility of choosing which pins are outputs and which are inputs. This may apply to all or some of the ports. Some I/O lines are suitable for direct interfacing to, for example, fluorescent displays, or can provide sufficient current to make interfacing other ponents straightforward. Some devices allow an I/O port to be configured as a system bus to allow offchip memory and I/O expansion. This facility is potentially useful as a product range develops, since successive enhancements may bee too big for onchip memory and it is undesirable not to build on the existing software base.Serial input/outputSerial munication with terminal devices is mon means of providing a link using a small number of lines. This sort of munication can also be exploited for interfacing special function chips or linking several microputers together .Both the mon asynchronous synchronous munication schemes require protocols that provide framing (start and stop) information .This can be implemented as a hardware facility or U(S) ART (Universal (synchronous)