Omron SYSMAC CP Series, User Manual

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3 CPU Unit Operation
3-2
CP2E CPU Unit Software User’s Manual(W614)
3-1 CPU Unit Operation
This section gives an overview of the CPU Unit operation, describes the operating modes, and explains
how the Unit operates when there is a power interruption.
The CPU Unit reads and writes data to the internal I/O memory areas while executing user ladder pro-
grams by executing the instructions in order one at a time from the start to the end.
Self-diagnosis, such as an I/O bus check, is performed.
Instructions are executed from the beginning of the program and I/O memory is refreshed.
Data to and from external devices, such as sensors and switches, directly connected to the built-in I/O
terminals and expansion I/O terminals, is exchanged with data in the I/O memory of the PLC. This pro-
cess of data exchange is called the I/O refresh.
Peripheral servicing is used to communicate with devices connected to the communications port or for
exchanging data with the CX-Programmer.
The cycle time is the time between one I/O refresh and the next.
3-1-1 Overview of CPU Unit Operation
Overhead Processing (Self-diagnosis)
Ladder Program Execution
I/O Refresh
Peripheral Servicing
Cycle Time
0 0 1 1 1 0 1 0
1 1 0 1 1 0 0 0
1 0 1 0 1 0 0 1
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
1 0 1 1 1 0 1 1
1 1 0 0 1 0 1 0
1 0 0 0 1 1 0 1
0 1 0 1 0 1 0 0
0 1 1 0 1 0 1 0
CPU Unit Internal Memory
CPU Unit
processing
cycle
O v erhead processing
(self-diagnosis)
Program exec u tion
I/O refreshing
Peripheral ser v icing
Access
I/O memory
Change in stat u s
after all instr u ctions
ha v e b een exec u ted
Exchange
Refreshes external de v ices at this timing
Inp u ts
O u tp u ts