Step 3 The CPU executes internal test by combining the instruction from Step 1

Step 3 the cpu executes internal test by combining

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Step 3 – The CPU executes internal test by combining the instruction from Step 1 with the information obtained from step 2. Step 4 – The CPU checks the user program memory if next instruction is another examine instruction . If it is another examine instruction, the CPU checks if it is logically ANDded or ORed with the previous instruction. If the next instruction is logically ANDed with the previous one, then both instructions must produce continuity for the rung to maintain continuity. If the next instruction is logically ORed with the previous one, then it is sufficient for either instruction to provide continuity in order for the rung to maintain continuity. Step 5 – The CPU determines if the overall rung conditions are true or false , and then it fetches the output energize instruction from the user program memory, so it could determine which output address/es to affect.
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Processor Section Step 6 – The CPU now knows the rung condition and output address/es to be affected, and it sends the proper digital signal to the output image file, which then passes the digital signal to the associated output terminal. After completing the execution of an instruction rung, it fetches and then executes the next sequential instruction from the user program memory. Below is a figure which shows the repetitive process being done by the PLC as long as it is in the RUN mode . Input Scan Output Scan Last Program Instruction User Program Instruction First Program Instruction
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