Chapter 5 Program Configuration and Operation Method
Chapter 5 Program Configuration and Operation Method
5.1.1 Program execution methods
(1) Cyclic operation method (Scan)
This is a basic program proceeding method of PLC that performs the operation repeatedly for the prepared
program from the beginning to the last step, which is called ‘program scan’. The series of processing like
this is called ‘cyclic operation method’. The processing is divided per stage as below.
Stage Processing description
A stage to start the scan processing which is executed once
when power is applied or Reset is executed, as below.
Self-diagnosis execution
Data clear
Address allocation of I/O module and type register
If initializing task is designated, Initializing program is executed.
Reads the state of input module and saves it in input image
area before starting the operation of program.
Performs the operation in order from the program start to last
step.
Performs the operation in order from the program start to last step.
A processing stage to return to the first step after CPU module
completes 1 scan processing and the processing performed is as
below.
Update the current value of timer and counter etc.
User event, data trace service
Self-diagnosis
High speed link, P2P e-Service
Check the state of key switch for mode setting
Start
Initialization processing
Input image area refresh
Program operation processing
Program start
Program last step
Output image area refresh
END
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