Chapter 5 Program Configuration and Operation Method
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Chapter 5 Program Configuration and Operation Method
5.1 Program Instruction
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
Start
Initialization processing
Input image area refresh
Program operation processing
Program start
Program last step
Output image area refresh
END
y
A stage to start the scan processing which is executed once when
power is applied or Reset is executed, as below.
I/O module reset
Self-diagnosis execution
Data clear
Address allocation of I/O module and type register
y
Performs the operation in order from the program start to last
step.
y
If the operation of program is completed, it prints out the
contents saved in output image area to output module.
y
Reads the state of input module and saves it in input image
area before starting the operation of program.
y
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
