單片機(jī)畢業(yè)外文翻譯-文庫吧在線文庫
【正文】 unction 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) asynchronous receiver/transmitter) relieving the processor (and the applications programmer) of this lowlevel, timeconsuming, detail. t is merely necessary to selected a baudrate and possibly other options (number of stop bits, parity, etc.) and load (or read from) the serial transmitter (or receiver) buffer. Serialization of the data in the appropriate format is then handled by the hardware circuit.Timing/counter facilities Many application of singlechip microputers require accurate evaluation of elapsed real time .This can be determined by careful assessment of the execution time of each branch in a program but this rapidly bees inefficient for all but simplest programs .The preferred approach is to use timer circuit that can independently count precise time increments and generate an interrupt after a preset time has elapsed .This type of timer is usually arranged to be reloadable with the required count .The timer then decrements this value producing an interrupt or setting a flag when the counter reaches zero. Better timers then have the ability to automatically reload the initial count value. This relieves the programmer of the responsibility of reloading the counter and assessing elapsed time before the timer restarted ,which otherwise wound be necessary if continuous precisely timed interrupts were required (as in a clock ,for example).Sometimes associated with timer is an event counter. With this facility there is usually a special input pin , that can drive the counter directly. Timing ponents The clock circuitry of most microputers requires only simple timing ponents. If maximum performance is required, a crystal must be used to ensure the maximum clock frequency is approached but not exceeded. Many clock circuits also work with a resistor and capacitor as lowcost timing ponents or can be driven from an external source. This latter arrangement is useful is external synchronization of the microputer is required. Programming languages Higher level PLC programming languages have been around for some time, but lately their popularity has mushrooming. As Raymond Leveille, vice president amp。s increasing use such industries as food ,chemicals ,and petroleum. Ryan feels there are two types of applications in which they39。s PLCs don39。這兩種特性在單片機(jī)中得到了充分的體現(xiàn)。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器）插座或存儲器相兼容，而不是ROM器件。中央處理單元（CPU）CPU 跟微處理器很相像。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。然后由硬件電路完成適當(dāng)格式的數(shù)據(jù)序列化處理。有時候與定時器相關(guān)的是一個事件計數(shù)器。舉例來說，很難寫三角函數(shù)使用梯形邏輯?！爸?，”他說，“是其中的過程控制系統(tǒng)，目前已被沒有理由自動化DCS的大小[分布式控制系統(tǒng)]隨著價格標(biāo)簽開始。拉里科馬雷克說：“現(xiàn)在，規(guī)范仍然是一個移動目標(biāo)，規(guī)范沒有最終決定，對于制造商。通用的I / O然而大多數(shù)PLC的兼容問題不同廠商的溝通不夠，在另一端連接的I/O問題，更是支離破碎的。當(dāng)然每個PLC供應(yīng)商將試圖保護(hù)這一點。朱迪格洛爾，市場經(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)”。各個獨立I/O制造商都在同一方向進(jìn)發(fā)。 例如Omron，擁有一個完整的兼容程序?！盉ill Barkovitz， Triconex的總統(tǒng)，預(yù)言：“今后所有的控制器在過程控制系統(tǒng)的業(yè)務(wù)將引用更多的PLC技術(shù)， PLC功能比以往任何時候都要多?！?Jannotta說。許多時鐘電路，還具有電阻和低電容工作成本定時元件，也可以從外部源驅(qū)動。這種類型的定時器通常在所要求的數(shù)量可重載中應(yīng)用。
環(huán)評公示相關(guān)推薦
鄂ICP備17016276號-1