6ES5340-3KB31
6ES5340-3KB31
6SC6101-2B-Z
6GK1500-0AB00
PLC執(zhí)行程序的過程分為三個階段,即輸入采樣階段、程序執(zhí)行階段、輸出刷新階段,PLC的掃描工作過程:
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公司全稱:
福州卓凱電子科技有限公司
公司地址:
福建省福州市閩侯西江濱大道77號正榮潤園1號樓1205室
(1)輸入采樣階段。在這一階段中,PLC以掃描方式讀入所有輸入端子上的輸入信號,并將各輸入狀態(tài)存入對應(yīng)的輸入映像寄存器中。此時,輸入映像寄存器被刷斷。在程序執(zhí)行階段和輸出刷新階段中,輸入映像存儲器與外界隔離,其內(nèi)容保持不變,直至下一個掃描周期的輸入掃描階段,才被重新讀入的輸入信號刷新。可見,PLC在執(zhí)行程序和處理數(shù)據(jù)時,不直接使用現(xiàn)場當(dāng)時的輸入信號,而使用本次采樣時輸入到映像區(qū)中的數(shù)據(jù)。一般來說,輸入信號的寬度要大于一個掃描周期,否則可能造成信號的丟失。
(2)程序執(zhí)行階段。在執(zhí)行用戶程序過程中,PLC按照梯形圖程序掃描原則,一般來說,PLC按從左至右、從上到下的步驟逐個執(zhí)行程序。但遇到程序跳轉(zhuǎn)指令,則根據(jù)跳轉(zhuǎn)條件是否滿足來決定程序跳轉(zhuǎn)地址。程序執(zhí)行過程中,當(dāng)指令中涉及輸入、輸出狀態(tài)時,PLC就從輸入映像寄存器中“讀入”對應(yīng)輸入端子狀態(tài),從輸出映像寄存器“讀入”對應(yīng)元件(“軟繼電器”)的當(dāng)前狀態(tài)。然后進行相應(yīng)的運算,運算結(jié)果再存入輸出映像寄存器中。對輸出映像寄存器來說,每一個元件(“軟繼電器”)的狀態(tài)會隨著程序執(zhí)行過程而變化。
(3)輸出刷新階段。程序執(zhí)行階段的運算結(jié)果被存入輸出映像區(qū),而不送到輸出端口上。在輸出刷新階段,PLC將輸出映像區(qū)中的輸出變量送入輸出鎖存器,然后由鎖存器通過輸出模塊產(chǎn)生本周期的控制輸出。如果內(nèi)部輸出繼電器的狀態(tài)為“1”,則輸出繼電器觸點閉合,經(jīng)過輸出端子驅(qū)動外部負載。全部輸出設(shè)備的狀態(tài)要保持一個掃描周期。
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