Mitsubishi Electronics 700 Series, FR-A700 Operation Processing Method of PLC Function

Operation Processing Method of PLC Function

3.5 Operation Processing Method of PLC Function

The operation processing method is the repeated operation of a stored program.

(1)Stored program system

1)In a stored program system, a sequence program to be operated is stored in the internal memory beforehand.

2)When sequence program operation is executed, the sequence program stored in the built-in PLC function is read to the CPU instruction by instruction to execute the operation, and the corresponding devices are controlled according to the results.

(2)Repeated operation system

In a repeated operation system, a sequence of operations is repeated. The built-in PLC function repeats the following processings.

1)The built-in PLC function executes the sequence program stored in the internal memory from step 0 in due order.

2)When the END instruction is executed, internal processings, such as timer/ counter present value updating and self-diagnostic checks, are performed, and the execution returns to step 0 of the sequence program again.

Step 0

Step 1

Step 2

Built-in sequence function repeats this operation.

END

Timer/counter present value updating Self-diagnostic checks, etc.

Fig 3.5 Operation Processing Method of Built-in PLC Function

REMARKS

A processing from step 0 to next step 0 or from END to next END is called one scan. Therefore, one scan is the sum of the processing time of a user-created program (step 0 to END) and the internal processing time of the built-in PLC function.

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