Omron CJ1W-SCU32 Operation Manual page 85

User-defined variable
The user program uses user-defined variables to access the storage area for the send/receive data, or
holding resisters and other allocation areas in the Modbus-RTU Slave Mode, with a communications
instruction.
For allocation of user-defined variables, refer to How to Create User-defined Variables (P. 2-13).
System-defined variable
These variables are allocated with specific functions pre-defined by the system.
Some are set automatically by the system and others are set and manipulated with the user program.
The Serial Communications Unit uses them to restart the Unit, change the communications setting, or
restart a serial communications port.
For details, refer to 2-4 System-defined Variable.
CJ-series Serial Communications Units Operation Manual for NJ-series CPU Unit(W494)
2 Initial Settings and Allocations of Device Variable for CJ-series Unit
2
2-11