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S7-200西門子_Siemens_PLC_電氣_中英文翻譯_畢業(yè)論文外文翻譯譯文S7-200的特性S7-200提供了幾條特殊的性能幫助您更好地運(yùn)用S7-200的功能,完成應(yīng)用程序。S7-200允許您在程序中立即讀寫I/O在S7-200的指令集中提供了立即讀寫物理I/O點(diǎn)的指令。盡管通常情況下我們使用映像寄存器作為源地址和目的地址來訪問I/O,但這些立即I/O指令卻允許我們直接訪問真正的輸入、輸出點(diǎn)。當(dāng)使用立即指令訪問一個(gè)輸入點(diǎn)時(shí),相應(yīng)的過程映像輸入寄存器不會(huì)發(fā)生改變。而當(dāng)您使用立即指令訪問一個(gè)輸出點(diǎn)時(shí),相應(yīng)的過程映像輸出寄存器會(huì)被同步刷新。提示除非您啟用了模擬量輸入濾波功能,否則S7-200將直接從模塊上讀取模擬量輸入值。當(dāng)您將一個(gè)數(shù)值寫到模擬量輸出時(shí),輸出值會(huì)立即更新。通常認(rèn)為在執(zhí)行應(yīng)用程序時(shí),用過程映像寄存器會(huì)比使用直接訪問輸入、輸出具有優(yōu)越性。之所以這樣有以下三個(gè)原因: 1.所有輸入點(diǎn)的采樣是在掃描周期的一開始同步進(jìn)行的。在整個(gè)掃描周期的程序執(zhí)行過程中輸入值被凍結(jié)。而輸出點(diǎn)按照映像寄存器中的值刷新是在程序執(zhí)行完成之后。這樣會(huì)使系統(tǒng)更加穩(wěn)定。 2.訪問映像寄存器的速度比直接訪問I/O點(diǎn)要快,有利于程序快速運(yùn)行。 3. I/O點(diǎn)是位實(shí)體,只能按位或者字節(jié)來訪問,而您可以按位、字節(jié)、字或者雙字的形式來訪問映像寄存器。通過這種方式,映像寄存器將為您提供額外的靈活性。S7-200允許在程序掃描周期中使用中斷如果您使用了中斷,與中斷事件相關(guān)的中斷程序作為程序的一部分被保存。中斷程序并不作為正常掃描周期的一部分來執(zhí)行,而是當(dāng)中斷事件發(fā)生時(shí)才執(zhí)行(可能在掃描周期的任意點(diǎn))。在中斷優(yōu)先級相同的情況下,S7-200遵循先來先服務(wù)的原則來執(zhí)行中斷程序。S7-200允許您為運(yùn)行模式編輯和執(zhí)行狀態(tài)分配處理時(shí)間您可以設(shè)定一個(gè)掃描周期的百分比用來處理運(yùn)行模式編輯或執(zhí)行狀態(tài)相關(guān)的通訊請求。(運(yùn)行模式編輯和執(zhí)行狀態(tài)是STEP 7-Micro/WIN提供的備選功能,能使您更輕松地調(diào)試程序。) 在您增加用于通訊請求處理時(shí)間百分比的同時(shí),掃描時(shí)間也會(huì)隨之增加,從而會(huì)導(dǎo)致控制過程運(yùn)行速度變慢。在默認(rèn)設(shè)置下,用于處理運(yùn)行模式編輯和執(zhí)行狀態(tài)通訊請求的時(shí)間百分比為10%。這個(gè)默認(rèn)設(shè)置為在對控制過程影響最小的前提下處理編譯和狀態(tài)操作,提供了一個(gè)合理的時(shí)間。您可以在5%到50%之間調(diào)節(jié)這個(gè)值。要想設(shè)置背景通訊的掃描周期時(shí)間片,按以下步驟:1. 點(diǎn)選視圖 組件 系統(tǒng)塊菜單命令并選中“背景時(shí)間”。2. 在“背景”標(biāo)簽下,通過下拉選框選擇通訊背景時(shí)間。3. 點(diǎn)擊“確定”保存您的選擇。4. 將改變后的系統(tǒng)塊下載到S7-200中。圖1 通訊背景時(shí)間S7-200允許您設(shè)置停止模式下的數(shù)字量輸出狀態(tài)S7-200的輸出表允許您選擇STOP模式下的輸出狀態(tài),是將已知值傳送到數(shù)字量輸出點(diǎn),還是使輸出保持STOP模式之前的狀態(tài)。輸出表是系統(tǒng)塊的一部分,它被下載并儲(chǔ)存在S7-200中。1. 選擇視圖 組件 系統(tǒng)塊菜單命令并選擇輸出表。點(diǎn)擊“數(shù)字量”標(biāo)簽。2. 如果要凍結(jié)上一個(gè)狀態(tài)的輸出,選擇“凍結(jié)輸出”復(fù)選框。3. 如果要將輸出表中的值復(fù)制到輸出點(diǎn)上,則要填寫輸出表。在您希望從運(yùn)行到停止模式轉(zhuǎn)換后置1的相應(yīng)位置上點(diǎn)擊。輸出表的缺省設(shè)置全部為0。4. 點(diǎn)擊“確定”保存您的選擇。5. 將改變后的系統(tǒng)塊下載到S7-200中。圖2 數(shù)字量輸出表S7-200允許您設(shè)置模擬量輸出值模擬量輸出表可以用來設(shè)置模擬量輸出點(diǎn),指明在從運(yùn)行模式進(jìn)入停止模式后,是將已知值傳送至模擬量輸出點(diǎn),還是使輸出保持停止模式之前的狀態(tài)。模擬量輸出表是下載并儲(chǔ)存在S7-200中的系統(tǒng)塊的一部分。1. 選擇視圖 組件 系統(tǒng)塊菜單命令并選擇“輸出表”。點(diǎn)擊“模擬量”標(biāo)簽。2. 如果要凍結(jié)上一個(gè)狀態(tài)的輸出,選擇“凍結(jié)輸出”復(fù)選框。3. 在從運(yùn)行模式進(jìn)入停止模式時(shí),通過凍結(jié)值表,您可以將模擬量輸出點(diǎn)設(shè)為一個(gè)已知值(-32768到37262)。4. 點(diǎn)擊“確定”保存您的選擇。5. 將改變后的系統(tǒng)塊下載到S7-200中。圖3 模擬量輸出表S7-200允許您定義掉電保護(hù)存儲(chǔ)區(qū)如果您希望在掉電后仍然保持存儲(chǔ)區(qū)中的數(shù)據(jù),您可以定義最多六個(gè)掉電保護(hù)區(qū)的地址范圍。可以將下列存儲(chǔ)區(qū)中的地址范圍定義為具有保持性:V、M、C和T。對于定時(shí)器,只有保持型定時(shí)器(TONR)可以設(shè)為掉電保護(hù)的。在缺省情況下,M存儲(chǔ)器的前14個(gè)字節(jié)是非保持的。只能保留定時(shí)器和計(jì)數(shù)器的當(dāng)前值:定時(shí)器和計(jì)數(shù)器位不具有保持性。提示如果將地址范圍MB0至MB13定義為保持,則在掉電時(shí),這個(gè)區(qū)域里的值就會(huì)自動(dòng)保存到永久存儲(chǔ)器中。按照以下步驟設(shè)置掉電保護(hù)區(qū):1. 點(diǎn)選視圖 組件 系統(tǒng)塊菜單命令并選中“保留范圍”。2. 設(shè)置掉電保護(hù)區(qū)的范圍并單擊“確定”。3. 將改變后的系統(tǒng)塊下載到S7-200中。圖4 保持存儲(chǔ)器S7-200允許對數(shù)字量輸入進(jìn)行過濾S7-200允許您為某些或者全部本機(jī)數(shù)字量輸入點(diǎn)選擇輸入濾波器,并為濾波器定義延遲時(shí)間(從0.2ms到12.8ms可選)。這一延遲時(shí)間有助于濾除輸入雜波,從而減小了輸入狀態(tài)發(fā)生意外改變的可能。輸入濾波器是系統(tǒng)塊的一部分,它被下載并存儲(chǔ)在CPU中。濾波器延遲時(shí)間的缺省值為6.4 ms。如圖5所示,一組輸入點(diǎn)共用一個(gè)延遲時(shí)間。按照以下步驟設(shè)置輸入濾波器延遲時(shí)間:1. 點(diǎn)選視圖 組件 系統(tǒng)塊菜單命令并選中“輸入濾波器”。點(diǎn)擊“數(shù)字”標(biāo)簽。2. 為每一組輸入指定延遲時(shí)間。3. 將改變后的系統(tǒng)塊下載到S7-200中。圖5 數(shù)字輸入濾波器提示數(shù)字量輸入濾波器會(huì)對讀取輸入指令、輸入中斷和脈沖捕獲產(chǎn)生影響。根據(jù)您的選擇,應(yīng)用程序有可能丟掉一個(gè)中斷事件或者脈沖捕獲。高速計(jì)數(shù)器不受此影響。S7-200允許您對模擬量輸入加濾波器S7-200允許您對每一路模擬量輸入選擇軟件濾波器。濾波值是多個(gè)模擬量輸入采樣值的平均值。濾波器參數(shù)(采樣次數(shù)和死區(qū))對于允許濾波的所有模擬量輸入是相同的。濾波器具有快速響應(yīng)的特點(diǎn),可以反映信號的快速變化。當(dāng)輸入與平均值的差超過設(shè)定的變化時(shí),濾波器對最近的模擬量輸入值產(chǎn)生一個(gè)階躍函數(shù)。這個(gè)差稱為死區(qū),并用模擬量輸入的數(shù)字信號設(shè)定。缺省組態(tài)將對所有的模擬量輸入進(jìn)行濾波,但CPU224XP上的AIW0和AIW2除外。1. 點(diǎn)選視圖 組件 系統(tǒng)塊菜單命令并選中“輸入濾波器”。點(diǎn)擊“模擬量”標(biāo)簽。2. 選擇需要濾波的模擬量輸入、采樣個(gè)數(shù)和死區(qū)。3. 單擊“確定”。4. 將改變后的系統(tǒng)塊下載到S7-200中。圖6 模擬量輸入濾波器提示不要對在模擬量字中傳遞數(shù)字信息或者報(bào)警指示的模塊使用模擬量輸入濾波。對于RTD、TC和ASI主站模塊,不能使用模擬量輸入濾波。提示CPU224XP上的AIW0和AIW2由模數(shù)轉(zhuǎn)換器來濾波,且通常無需另外的軟件濾波。S7-200允許您捕捉窄脈沖S7-200為每個(gè)本機(jī)數(shù)字量輸入提供脈沖捕獲功能。脈沖捕獲功能允許PLC捕捉到持續(xù)時(shí)間很短的高電平脈沖或者低電平脈沖。而在掃描周期的開始,這些脈沖不是總能被CPU讀到。當(dāng)一個(gè)輸入設(shè)置了脈沖捕獲功能時(shí),輸入端的狀態(tài)變化被鎖存并一直保持到下一個(gè)掃描循環(huán)刷新。這就確保了一個(gè)持續(xù)時(shí)間很短的脈沖能被捕捉到,并一直保持到S7-200讀取輸入點(diǎn)??梢苑謩e啟用每一個(gè)本機(jī)數(shù)字量輸入點(diǎn)的脈沖捕獲功能。按照以下步驟設(shè)置脈沖捕獲:1. 點(diǎn)選視圖 組件 系統(tǒng)塊菜單命令并選中“脈沖捕獲位”。2. 點(diǎn)擊相應(yīng)的復(fù)選框并點(diǎn)擊“確定”。3. 將改變后的系統(tǒng)塊下載到S7-200中。圖7 脈沖捕獲在啟用或禁止脈沖捕獲的情況下,S7-200可進(jìn)行的基本操作如圖8所示。圖8 帶有和不帶有脈沖捕獲功能的S7-200操作由于脈沖是在通過了輸入濾波器之后,才能夠被捕捉到,因而要調(diào)整輸入濾波時(shí)間,確保脈沖不被濾掉。圖9 為數(shù)字量輸入電路的方框圖。圖9 數(shù)字量輸入電路對于不同的輸入條件,脈沖捕獲功能的響應(yīng)如圖10所示。如果在給定的掃描周期中有不止一個(gè)脈沖,則只有第一個(gè)脈沖被讀到。這種情況下,您應(yīng)該使用上升/下降沿中斷事件。圖10 不同輸入條件下的脈沖捕獲響應(yīng)S7-200的用戶控制LEDS7-200提供了一個(gè)可以發(fā)紅光(系統(tǒng)故障LED)或黃光(診斷LED)的LED(SF/DIAG)。診斷LED可在用戶程序控制下點(diǎn)亮,或在某些條件下自動(dòng)點(diǎn)亮:當(dāng)強(qiáng)行施加I/O點(diǎn)或數(shù)據(jù)值時(shí),或當(dāng)模塊出現(xiàn)I/O錯(cuò)誤時(shí)。設(shè)置診斷LED自動(dòng)點(diǎn)亮:1. 點(diǎn)選視圖 組件 系統(tǒng)塊菜單命令并選中“組態(tài)LED”。2. 點(diǎn)擊各選項(xiàng),以指定在I/O點(diǎn)或數(shù)據(jù)被強(qiáng)制,或者模塊發(fā)生I/O錯(cuò)誤時(shí),LED是否點(diǎn)亮。3. 將改變后的系統(tǒng)塊下載到S7-200中。圖11 診斷LEDS7-200保留一份關(guān)于主要CPU事件的歷史歸檔S7-200會(huì)保留一份關(guān)于主要CPU事件的歷史歸檔,該歸檔帶有時(shí)間標(biāo)記,所歸檔的內(nèi)容包括:何時(shí)上電、CPU何時(shí)進(jìn)入運(yùn)行模式,以及何時(shí)出現(xiàn)致命錯(cuò)誤。在設(shè)置了實(shí)時(shí)時(shí)鐘之后,歸檔條目就會(huì)帶有正確的時(shí)間和日期。要查看事件歷史歸檔,可點(diǎn)擊PLC 信息菜單命令并選擇“事件歷史”。圖12 查看事件歷史歸檔S7-200允許您增大可用用戶程序存儲(chǔ)器在S7-200的CPU224、CPU 224XP和CPU226上,您可以禁用運(yùn)行模式編輯功能,從而增大可用用戶程序存儲(chǔ)器的容量。要禁用運(yùn)行模式編輯功能,可執(zhí)行以下步驟:1. 點(diǎn)選視圖 組件 系統(tǒng)塊菜單命令并選中“增加程序存儲(chǔ)器容量”。2. 點(diǎn)擊“增加存儲(chǔ)器容量”選項(xiàng),禁用運(yùn)行模式編輯。3. 將改變后的系統(tǒng)塊下載到S7-200中。圖13 禁用運(yùn)行模式編輯S7-200提供口令保護(hù)功能S7-200的所有型號都提供口令保護(hù)功能,用以限制對特殊功能的訪問??诹钍跈?quán)對功能和存儲(chǔ)器進(jìn)行訪問:沒有口令時(shí),S7-200提供不受限的訪問。設(shè)置了口令保護(hù),根據(jù)安裝口令時(shí)的設(shè)置,CPU禁止所有的受限操作??诹畈粎^(qū)分大小寫。如表1所示,S7-200 CPU提供了限制CPU訪問功能的四個(gè)等級。每個(gè)等級允許特定的無需口令的訪問功能。對于四個(gè)訪問級別,輸入正確的口令提供對下述功能的訪問。S7-200的缺省設(shè)置為等級1 (沒有限制)。在網(wǎng)絡(luò)中輸入口令不會(huì)對CPU的口令保護(hù)有所危害。由于級別1允許所有未受限CPU訪問,因此,可通過將口令級4、3或2改為1級,啟用或禁止口令。表1 限制對S7-200的訪問授權(quán)一個(gè)用戶訪問PLC信息中的受限功能“復(fù)位掃描速率”并不意味著授權(quán)其他用戶訪問這些功能。同一時(shí)刻,只允許一個(gè)用戶不受限制地訪問CPU。提示當(dāng)輸入口令后,在編程設(shè)備同CPU斷開連接的一分鐘之內(nèi),該授權(quán)等級仍然有效。在斷開連接電纜之前,一定要先退出STEP7-Micro/WIN,以避免其他用戶利用編程設(shè)備訪問CPU。為S7-200組態(tài)口令如圖14所示的系統(tǒng)塊對話框允許您為S7-200組態(tài)口令。S7-200的缺省設(shè)置是“完全”(1級),沒有任何限制。1. 選擇視圖 組件 系統(tǒng)塊菜單命令,彈出“系統(tǒng)塊”對話框并選擇“口令”。2. 為S7-200選擇合適的訪問級別。3. 輸入并確認(rèn)“部分”(2級)或“最低”(3級)口令。4. 單擊“確定”。5. 將改變后的系統(tǒng)塊下載到S7-200中。圖14 創(chuàng)建口令口令忘記后如何恢復(fù)如果您忘記了口令,您必須清除S7-200的存儲(chǔ)器,重新下載應(yīng)用程序。清除存儲(chǔ)器會(huì)使S7-200處于停止模式,并且將S7-200中,除了網(wǎng)絡(luò)地址、波特率和時(shí)鐘以外的其他參數(shù)恢復(fù)到出廠設(shè)置。清除S7-200中的程序:1. 在命令菜單中選擇PLC 清除來顯示清除對話框。2. 選擇所有的塊并點(diǎn)擊“確定”確認(rèn)。3. 如果組態(tài)了口令,STEP7-Micro/WIN會(huì)顯示口令授權(quán)對話框。要清除口令,在口令授權(quán)對話框中輸入“CLEARPLC”,就可以繼續(xù)執(zhí)行全部清除的操作。(“CLEARPLC”不區(qū)分大小寫。)全部清除操作不會(huì)去掉存儲(chǔ)卡中的程序。由于口令和程序一同保存在存儲(chǔ)卡中,因而必須重新寫存儲(chǔ)卡,才能從程序中去掉口令。警告清除S7-200存儲(chǔ)器會(huì)導(dǎo)致輸出關(guān)閉(對于模擬量輸出來說,會(huì)被凍結(jié)在某個(gè)特定值)。當(dāng)清除S7-200存儲(chǔ)器時(shí),如果S7-200與其他設(shè)備相連,則輸出狀態(tài)的變化會(huì)傳遞到該設(shè)備。如果輸出的“安全狀態(tài)”與廠家設(shè)定不同,輸出的變化可能會(huì)引起設(shè)備產(chǎn)生不可預(yù)料的動(dòng)作,也可能導(dǎo)致死亡或嚴(yán)重的人身傷害和設(shè)備損壞。在清除S7-200存儲(chǔ)器之前,必須有合適的安全預(yù)防措施,確保您的操作是安全的。S7-200提供模擬電位計(jì)模擬電位計(jì)位于模塊前蓋下面。您可以調(diào)節(jié)這些電位計(jì)來增加或者減小存于特殊存儲(chǔ)器中的值(SMB)。這些只讀值在程序中可用作很多功能,如更新定時(shí)器或計(jì)數(shù)器的當(dāng)前值,輸入或修改預(yù)設(shè)值、限定值等。使用一個(gè)小螺絲起子進(jìn)行調(diào)節(jié):順時(shí)針轉(zhuǎn)動(dòng)電位計(jì)(向右)增大數(shù)值,逆時(shí)針轉(zhuǎn)動(dòng)(向左)減小數(shù)值。SMB28 保持代表模擬調(diào)節(jié)0的位置的數(shù)值。SMB29保持代表模擬調(diào)節(jié)1的位置的數(shù)值。模擬調(diào)節(jié)的額定范圍是0-255,重復(fù)計(jì)數(shù) 2次。S7-200提供高速I/O高速計(jì)數(shù)器S7-200具有集成的高速計(jì)數(shù)功能,它能夠?qū)ν獠扛咚偈录?jì)數(shù)而不影響S7-200的性能。不同CPU支持的計(jì)數(shù)速率,參見附錄A。每個(gè)計(jì)數(shù)器有用于時(shí)鐘、方向控制、復(fù)位和啟動(dòng)的專用輸入,這種情況下可支持這些功能。在不同的模式下有不同的計(jì)數(shù)速率。高速脈沖輸出S7-200支持高速脈沖輸出功能,其輸出點(diǎn)Q0.0和Q0.1可形成高速脈沖串輸出(PTO)或脈寬調(diào)制(PWM)。PTO輸出方波(占空比50%),并可指定所輸出的脈沖數(shù)量(從1到4,294,967,295)和周期(以微秒或毫秒為單位)。脈沖序列輸出(PTO)功能可以編程為產(chǎn)生一列脈沖或產(chǎn)生由多個(gè)脈沖序列組成的脈沖包絡(luò)。在脈沖包絡(luò)操作方式中,PTO功能被編程為控制一個(gè)步進(jìn)電機(jī)運(yùn)行一個(gè)簡單的斜坡上升、運(yùn)行和斜坡下降操作序列或更復(fù)雜的操作序列。PWM功能提供具有可變占空比的固定周期的輸出脈沖,周期和脈寬既可以用微秒又可以用毫秒為單位。當(dāng)脈寬等于周期時(shí),占空比為100,輸出恒定為1; 當(dāng)脈寬等于0時(shí),占空比為0,輸出恒定為0。外文翻譯原文Features of the S7-200The S7-200 provides several special features that allow you to customize how the S7-200 functions to better fit your application.The S7-200 Allows Your Program to Immediately Read or Write the I/OThe S7-200 instruction set provides instructions that immediately read from or write to the physical I/O. These immediate I/O instructions allow direct access to the actual input or output point, even though the image registers are normally used as either the source or the destination for I/O accesses.The corresponding process-image input register location is not modified when you use an immediate instruction to access an input point. The corresponding process-image output register location is updated simultaneously when you use an immediate instruction to access an output point.TipThe S7-200 handles reads of analog inputs as immediate data, unless you enable analog input filtering. When you write a value to an analog output, the output is updated immediately.It is usually advantageous to use the process-image register rather than to directly access inputs or outputs during the execution of your program. There are three reasons for using the image registers: - The sampling of all inputs at the start of the scan synchronizes and freezes the values of the inputs for the program execution phase of the scan cycle. The outputs are updated from the image register after the execution of the program is complete. This provides a stabilizing effect on the system. - Your program can access the image register much more quickly than it can access I/O points, allowing faster execution of the program. - I/O points are bit entities and must be accessed as bits or bytes, but you can access the image register as bits, bytes, words, or double words. Thus, the image registers provide additional flexibility.The S7-200 Allows Your Program to Interrupt the Scan Cycle If you use interrupts, the routines associated with each interrupt event are stored as part of the program. The interrupt routines are not executed as part of the normal scan cycle, but are executed when the interrupt event occurs (which could be at any point in the scan cycle).Interrupts are serviced by the S7-200 on a first-come-first-served basis within their respective priority assignments. The S7-200 Allows You to Allocate Processing Time for Run Mode Edit and Execution Status You can configure a percentage of the scan cycle to be dedicated for processing a run mode edit compilation or execution status. (Run mode edit and execution status are options provided by STEP 7-Micro/WIN to make debugging your program easier.) As you increase the percentage of time that is dedicated to these two tasks, you increase the scan time, which makes your control process run more slowly. The default percentage of the scan dedicated to processing run mode edits and execution status is set to 10%. This setting was chosen to provide a reasonable compromise for processing the compilation and status operations while minimizing the impact to your control process. You can adjust this value by 5% increments up to a maximum of 50%. To set the scan cycle time-slice for background communications: 1. Select the View Component System Block menu command and select Background Time. 2. In the Background tab, use the drop down box to select the communications background time. 3. Click OK to save your selection. 4. Download the modified system block to the S7-200.Figure 1 Communications Background TimeThe S7-200 Allows You to Set the States of Digital Outputs for Stop Mode The output table of the S7-200 allows you to determine whether to set the state of the digital output points to known values upon a transition to the STOP mode, or to leave the outputs in the state they were in before the transition to the STOP mode. The output table is part of the system block that is downloaded and stored in the S7-200. 1. Select the View Component System Block menu command and select Output Table. Click on the Digital tab. 2. To freeze the outputs in their last state, select the Freeze Outputs checkbox. 3. To copy the table values to the outputs, enter the output table values by clicking the checkbox for each output bit you want to set to On (1) after a run-to-stop transition. The default values of the table are all zeroes. 4. Click OK to save your selections. 5. Download the modified system block to the S7-200.Figure 2 Digital Output TableThe S7-200 Allows You to Configure the Value of Analog Outputs The Analog Output Table allows you to set analog output points to known values after aRUN-to-STOP transition, or to preserve the output values that existed before the transition toSTOP mode. The Analog Output table is part of the system block that is downloaded and stored in the S7-200 CPU. 1. Select the View Component System Block menu command and select Output Table. Click on the Analog tab. 2. To freeze the outputs in their last state, select the Freeze Outputs check box. 3. The Freeze Values table allows you to set the analog outputs to a known value (-32768 to 37262), on a RUN-to-STOP transition. 4. Click OK to save your selections. 5. Download the modified system block to the S7-200.Figure 3 Analog Output TableThe S7-200 Allows You to Define Memory to Be Retained on Loss of Power You can define up to six retentive ranges to select the areas of memory you want to retain through power cycles. You can define ranges of addresses in the following memory areas to be retentive: V, M, C, and T. For timers, only the retentive timers (TONR) can be retained. The default setting for the first 14 bytes of M Memory is to be non-retentive. Only the current values for timers and counters can be retained: the timer and counter bits are not retentive. Tip Changing the range MB0 to MB13 to be retentive enables a special feature that automatically saves these locations to the permanent memory on power down. To define the retentive memory: 1. Select the View Component System Block menu command and select Retentive Ranges. 2. Select the ranges of memory to be retained following loss of power and click OK. 3. Download the modified system block to the S7-200.Figure 4 Retentive MemoryThe S7-200 Allows You to Filter the Digital Inputs The S7-200 allows you to select an input filter that defines a delay time (selectable from 0.2 ms to 12.8 ms) for some or all of the local digital input points. This delay helps to filter noise on the input wiring that could cause inadvertent changes to the states of the inputs. The input filter is part of the system block that is downloaded and stored in the S7-200. The default filter time is 6.4 ms. As shown in Figure 4, each delay specification applies to groups of input points. To configure the delay times for the input filter: 1. Select the View Component System Block menu command and select Input Filters. Click on the Digital tab. 2. Enter the amount of delay for each group of inputs and click OK. 3 Download the modified system 3. Download the modified system block to the S7-200. Tip The digital input filter affects the input value as seen by instruction reads, input interrupts, and pulse catches. Depending on your filter selection, your program could miss an interrupt event or pulse catch. The high speed counters count the events on the unfiltered inputs.The S7-200 Allows You to Filter the Analog Inputs The S7-200 allows you to select software filtering on individual analog inputs. The filtered value is the average value of a preselected number of samples of the analog input. The filter specification (number of samples and deadband) is the same for all analog inputs for which filtering is enabled. The filter has a fast response feature to allow large changes to be quickly reflected in the filter value. The filter makes a step function change to the latest analog input value when the input exceeds a specified change from the current value. This change, called the deadband, isspecified in counts of the digital value of the analog input. The default configuration is to enable filtering for all analog inputs except AIW0 and AIW2 on CPU 224XP. 1. Select the View Component System Block menu command and select Input Filters. Click on the Analog tab. 2. Select the analog inputs that you want to filter, the number of samples, and the deadband. 3. Click OK. 4. Download the modified system block to the S7-200.Figure 5 Analog Input Filter Tip Do not use the analog filter with modules that pass digital information or alarm indications in the analog words. Always disable analog filtering for RTD, Thermocouple, and AS-Interface Master modules. Tip AIW0 and AIW2 on the CPU 224XP are filtered by the analog to digital converter, and usually will not need the additional software filter.The S7-200 Allows You to Catch Pulses of Short DurationThe S7-200 provides a pulse catch feature which can be used for some or all of the local digital input points. The pulse catch feature allows you to capture high-going pulses or low-going pulses that are of such a short duration that they would not always be seen when the S7-200 reads the digital inputs at the beginning of the scan cycle. When pulse catch is enabled for an input, a change in state of the input is latched and held until the next input cycle update. This ensures that a pulse which lasts for a short period of time is caught and held until the S7-200 reads the inputs.You can individually enable the pulse catch operation for each of the local digital inputs.To access the pulse catch configuration screen:1. Select the View Component System Block menu command and select Pulse Catch Bits.2. Click the corresponding check box and click OK.3. Download the modified system block to the S7-200.Figure 6 Pulse CatchFigure 7 shows the basic operation of the S7-200 with and without pulse catch enabled.Figure 7 Operation of the S7-200 with the Pulse Catch Feature Enabled and DisabledBecause the pulse catch function operates on the input after it passes through the input filter, you must adjust the input filter time so that the pulse is not removed by the filter. Figure 8 shows a block diagram of the digital input circuit.Figure 8 Digital Input CircuitFigure 9 shows the response of an enabled pulse catch function to various input conditions. If you have more than one pulse in a given scan, only the first pulse is read. If you have multiple pulses in a given scan, you should use the rising/falling edge interrupt events. Figure 9 Responses of the Pulse Catch Function to Various Input ConditionsThe S7-200 Provides a User-Controlled LEDThe S7-200 provides an LED (SF/DIAG) that can indicate red (system fault LED) or yellow (diagnostic LED). The diagnostic LED can be illuminated under user program control, or can automatically illuminate under certain conditions: when an I/O point or data value is forced, or when a module has an I/O error.To configure the automatic selections for the diagnostic LED: 1. Select the View Component System Block menu command and select Configure LED. 2. Click each item to either enable or disable turning on the LED when an

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