产品标题:  F7553工控DCS系统备件模块

型号： F7553

品牌： HIMA

                                                                                 产品详情资料：

程序执行阶段

　　PLC的用户程序决定了输入信号与输出信号之间的具体关系。组成程序的每条指令都有顺序号，在PLC中称为步序号。指令按步序号依次存入存储单元。程序执行期间，在无跳转指令时，地址计数器顺序寻址，依次指向每个存储单元，控制器顺序执行这些指令。执行指令时先读入输入状态寄存器的状态，若程序中规定要读入某输出状态，也在此时从输出状态寄存器的某对应位读入，然后进行逻辑运算，运算结果存入输出状态寄存器。这就是说输出状态寄存器的内容，会伴随程序的执行而变化（由输出指令的执行结果所决定）。输出状态寄存器的位数与输出元件数目相对应，所以它又称为元件映象寄存器。

　　输出刷新阶段

　　在所有的指令执行完毕后，输出状态寄存器中的状态（即输出继电器的状态）在输出刷新阶段转存到输出锁存器锁存，驱动输出线圈，形成PLC的实际输出。

　　在一个周期执行完后，地址计数器恢复到初始值，重复执行由以上三个阶段构成的工作周期。

　　虽然可以把PLC看成一个用微处理机实现的许多电子式继电器、定时器和计数器的组合体；不过需要注意的是PLC与继电器开关电路在动作顺序上的差别。对于继电器开关电路，全部继电器的动作可以看成是并行执行的，或者说是同时执行的，而PLC的电器动作是按程序或者说是串行，按周期重复执行的。这使得PLC的输出对于输入存在滞后，因此在进行PLC程序设计时，应充分注意它的周期工作方式。

                          产品英文详情资料：

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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