3 CPU Unit Operation
3-2
CJ2 CPU Unit Software User’s Manual
3-1 CPU Unit Internal Operation
The CPU Unit writes data to the internal I/O memory areas while it cyclically executes user programs.
Data is exchanged externally when I/O is refreshed and peripherals are serviced. The following figure
shows the internal operation of the CPU Unit.
The following processes will be performed once each time the power is turned ON to the PLC.
• Detecting connected Units (I/O allocation)
• Comparing the registered I/O tables and the connected Units
• Clearing the non-holding areas in I/O memory according to the status of the IOM Hold Bit
• Clearing forced status according to the status of the Forced Status Hold Bit
• Autobooting using the autotransfer files in the Memory Card if one is inserted
• Performing self-diagnosis (user memory check)
• Restoring the user program
• Updating the PLC Setup
3-1-1 Overview
Startup Initialization
Startup initialization
(1) Overseeing processing
(2) Program execution
(4) I/O refreshing
(3) Peripheral servicing
Cycle
time
Pro-
cessing
cycle
Configuration
Units
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