產(chǎn)品標(biāo)題:  F7553工控DCS系統(tǒng)備件模塊

型號(hào)： F7553

品牌： HIMA

                                                                                 產(chǎn)品詳情資料：

程序執(zhí)行階段

　　PLC的用戶程序決定了輸入信號(hào)與輸出信號(hào)之間的具體關(guān)系。組成程序的每條指令都有順序號(hào)，在PLC中稱為步序號(hào)。指令按步序號(hào)依次存入存儲(chǔ)單元。程序執(zhí)行期間，在無跳轉(zhuǎn)指令時(shí)，地址計(jì)數(shù)器順序?qū)ぶ罚来沃赶蛎總€(gè)存儲(chǔ)單元，控制器順序執(zhí)行這些指令。執(zhí)行指令時(shí)先讀入輸入狀態(tài)寄存器的狀態(tài)，若程序中規(guī)定要讀入某輸出狀態(tài)，也在此時(shí)從輸出狀態(tài)寄存器的某對(duì)應(yīng)位讀入，然后進(jìn)行邏輯運(yùn)算，運(yùn)算結(jié)果存入輸出狀態(tài)寄存器。這就是說輸出狀態(tài)寄存器的內(nèi)容，會(huì)伴隨程序的執(zhí)行而變化（由輸出指令的執(zhí)行結(jié)果所決定）。輸出狀態(tài)寄存器的位數(shù)與輸出元件數(shù)目相對(duì)應(yīng)，所以它又稱為元件映象寄存器。

　　輸出刷新階段

　　在所有的指令執(zhí)行完畢后，輸出狀態(tài)寄存器中的狀態(tài)（即輸出繼電器的狀態(tài)）在輸出刷新階段轉(zhuǎn)存到輸出鎖存器鎖存，驅(qū)動(dòng)輸出線圈，形成PLC的實(shí)際輸出。

　　在一個(gè)周期執(zhí)行完后，地址計(jì)數(shù)器恢復(fù)到初始值，重復(fù)執(zhí)行由以上三個(gè)階段構(gòu)成的工作周期。

　　雖然可以把PLC看成一個(gè)用微處理機(jī)實(shí)現(xiàn)的許多電子式繼電器、定時(shí)器和計(jì)數(shù)器的組合體；不過需要注意的是PLC與繼電器開關(guān)電路在動(dòng)作順序上的差別。對(duì)于繼電器開關(guān)電路，全部繼電器的動(dòng)作可以看成是并行執(zhí)行的，或者說是同時(shí)執(zhí)行的，而PLC的電器動(dòng)作是按程序或者說是串行，按周期重復(fù)執(zhí)行的。這使得PLC的輸出對(duì)于輸入存在滯后，因此在進(jìn)行PLC程序設(shè)計(jì)時(shí)，應(yīng)充分注意它的周期工作方式。

                          產(chǎn)品英文詳情資料：

Program execution phase

The user program of PLC determines the specific relationship between input signals and output signals. Each instruction that constitutes a program has a sequence number, which is called a step number in PLC. The instructions are stored in the storage unit in sequence by step number. During program execution, when there are no jump instructions, the address counter sequentially addresses each storage unit, and the controller sequentially executes these instructions. When executing an instruction, the state of the input status register is first read in. If the program specifies that an output status should be read in, it is also read in from a corresponding bit of the output status register at this time, and then logical operations are performed. The operation results are stored in the output status register. This means that the content of the output status register will change with the execution of the program (determined by the execution result of the output instruction). The number of bits in the output status register corresponds to the number of output components, so it is also called a component image register.

Output refresh stage

After all instructions are executed, the state in the output status register (i.e. the state of the output relay) is transferred to the output latch during the output refresh stage, driving the output coil to form the actual output of the PLC.

After a cycle is completed, the address counter returns to its initial value and repeats the work cycle composed of the above three stages.

Although PLC can be seen as a combination of many electronic relays, timers, and counters implemented with microprocessors; However, it should be noted that there are differences in the action sequence between PLC and relay switch circuits. For relay switch circuits, the actions of all relays can be seen as being executed in parallel or simultaneously, while the electrical actions of PLC are executed in a program or serial manner, repeating the cycle. This causes the output of the PLC to lag behind the input, so when designing the PLC program, full attention should be paid to its periodic working mode.

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