Bit logic instruction is the most basic and frequently used instruction in PLC programming. It has different forms according to different functions and uses. Generally speaking, it can be divided into the following categories: standard bit logic instruction, set / reset instruction, immediate bit logic instruction and other bit logic instructions.

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Bit logic instruction classification

Standard bit logic command includes normally open contact, normally closed contact and output coil command; The set / reset instruction includes set instruction, reset instruction, set priority RS trigger instruction and reset priority RS trigger instruction; The immediate position logic command includes immediate normally open or immediate normally closed contact command, immediate output coil command, immediate set command and immediate reset command, all of which are marked with I; Other bit logic instructions include reverse instruction, rising edge instruction, falling edge instruction and null operation instruction.

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Standard bit logic instruction

Next, Changhui instrument will explain the use of next bit logic command by taking the start, maintenance and stop control program as an example. It is required to prepare the start and stop control program, that is, press the instantaneous button i0.0 to start the motor q0.0, and press the instantaneous button i0.1 to stop the motor q0.0. Firstly, Changhui instrument double-click the STEP7 micro / win smart programming software icon on the desktop to start the programming software, select a normally open contact from the bit logic command option in the command tree, drag and drop it into program section 1 of the program editor, input address i0.0 as the start contact, drag a normally closed contact in series with it, input address i0.1 as the stop contact, and drag and drop an output coil, The input address q0.0 is used as the output coil of the start / stop circuit.

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Drag and drop contacts and coils

Drag and drop a q0.0 normally open contact below the normally open contact i0.0, and click the insert upward vertical line button in the toolbar to connect it in parallel as a self-locking contact. In this way, the preparation of a simple start, protection and stop control program is completed. Compile and download the program to S7-200 smart. Click the download button in the menu, select the CPU to access in the open communication dialog box, click OK to download, and close the dialog box after downloading.

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Download program

Responsible editor: LQ

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