LS Industrial Systems XBC-E Series - 4.4 Program Instruction

Chapter 4 CPU Specifications
XBC E-Type Main Unit 4-5 Ver. 1
4.4 Program Instruction
4.4.1 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
-
• Starts the scan processing which is executed once when
power is applied or Reset is executed in the following events:
• I/O module reset
• 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 update
Program operation processing
Program start
Program last step
Output image update
END