ZCP270 P0926CP控制器輸入采樣階段。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?？梢?，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。

ZCP270–P0926CP-

ZCP270 P0926CP Controller input sampling phase. In this stage, the PLC reads input signals on all input terminals by scanning, and stores each input state into the corresponding input image register. At this point, the input image register is brushed off. During the program execution phase and the output refresh phase, the input image memory is isolated from the outside world and its contents remain unchanged until the input scan phase of the next scan cycle, when it is refreshed by the input signal that is re-read. It can be seen that when the PLC executes the program and processes the data, it does not directly use the input signal at the time of the scene, but uses the data input to the image area during this sampling. Generally speaking, the width of the input signal should be greater than one scan cycle, otherwise the signal may be lost.
(2) Program execution stage. In the process of executing the user program, the PLC scans according to the ladder diagram program principle, in general, the PLC executes the program one by one from left to right and from top to bottom. However, when the program jump instruction is encountered, the program jump address is determined according to whether the jump condition is met. During the execution of the program, when the input and output states are involved in the instruction, the PLC “reads” the corresponding input terminal state from the input image register, and “reads” the current state of the corresponding component (” soft relay “) from the output image register. Then the corresponding operation is performed and the result is stored in the output image register. For the output image register, the state of each component (the “soft relay”) changes as the program executes.
(3) Output refresh phase. The results of the program execution phase are stored in the output image area, and are not sent to the output port. In the output refresh stage, the PLC sends the output variables in the output image area to the output latch, and then the latch generates the control output of the cycle through the output module. If the status of the internal output relay is “1”, the output relay contact is closed and the external load is driven through the output terminal. The status of all output devices must be maintained for a scanning period.

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