可分为以下三个阶段，如下所述：1、输入处理程序执行前，可编程控制器的全

It can be divided into the following three stages, as follows: <br>1. <br>Before the input processing program is executed, the on/off status of all input terminals of the programmable controller is read into the input image register. During program execution, even if the input state changes, the content of the input shadow register does not change. This change is not read in until the input processing stage of the next scan cycle. In addition, the input contact changes from on (ON) to off (OFF) or from off (OFF) to on (ON) until it is in a certain state, and the input filter has a response delay time (about 10ms). <br>2. The program processes <br>the instructions stored in its corresponding user program memory, reads the on/off status of the relevant soft elements from the input shadow register and the shadow registers of other soft elements, starts the sequential operation from step 0, and writes the result every time The related shadow register, therefore, the content of the shadow register of each device (except X) is constantly changing with the execution of the program. <br>The action of the internal contact of the output relay is determined by the content of the output mirror register. <br>3, the output processing <br>all the instructions is finished, the ON / OFF state of the output register image transmitted to the output latch register <br>to send, to become the actual output of the PLC. <br>The external output contact of the programmable controller has a response time to the action of the output soft element, that is, there is a delay before the action.

It can be divided into three phases, as follows:<br>1, input processing<br>Before the program executes, the on/off state of all input terminals of the programmable controller is read into the input image register. In program execution, the contents of the input image register remain the same even if the input state changes. This change is not read into the input processing phase of the next scan cycle. In addition, the input contact changes from on (ON) off (0FF) or from off (0FF) pass (ON) to a definite state, and the input filter has a response delay time (approximately 10ms).<br>2, program processing<br>It corresponds to the instructions stored in the user program memory, reads out the on/off status of the soft element from the image register of the input image register and other soft elements, starts the sequence operation from 0 steps, and writes each result to the relevant image register, so the contents of the image registers of each soft element (except X) are constantly changing with the execution of the program.<br> The action of the internal contacts of the output relay is determined by the contents of the output image register.<br>3, output processing<br>When all instructions are executed, the on/off state of the output image register is transmitted to the output latch register<br>to become the actual output of the programmable controller.<br> The external output contacts of the programmable controller have a response time for the action of the output soft element, i.e. a delay is required before the action is required.

It can be divided into three stages as follows:<br>1. Input processing<br>Before the program is executed, the on / off status of all input terminals of PLC is read into the input image register. In the process of program execution, even if the input state changes, the content of the input image register remains unchanged. This change is not read in until the input processing phase of the next scan cycle. In addition, the input filter has a response delay time (about 10ms) when the input contact changes from on to off (0ff) or from off (0ff) to on.<br>2. Program processing<br>Corresponding to the instructions stored in the user program memory, the on / off status of the relevant software components is read out from the input image register and the image registers of other software components, and the sequential operation starts from step 0. The results are written into the relevant image registers each time. Therefore, the contents of the image registers of each software component (except x) are constantly changing with the execution of the program.<br>The action of the internal contact of the output relay is determined by the content of the output image register.<br>3. Output processing<br>After all instructions are executed, the on / off state of the output image register is transferred to the output latch register<br>Send, become the actual output of PLC.<br>The external output contact of PLC has a response time to the action of the output soft component, that is, it needs a delay to act.<br>