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7 Using Modbus-RTU Slave Mode
7-8
CJ-series Serial Communications Units Operation Manual for NJ-series CPU Unit(W494)
Additional Information
Addresses in Modbus data models start from 1, but addresses specified in Modbus-RTU com-
mands and addresses in the NJ-series Controller start from 0. Refer to the above table when
specifying addresses in applications.
z
Port 1/2 Settings Changing Flag
You can use an Out instruction or another instruction from the program to turn these flags to TRUE to
change communications settings and restart the Serial Communications Unit ports. After you change
the settings and restart the communications port, the flag will automatically be turned to FALSE.
Note These flag are used both to change the communications port settings and to restart the com-
munications port at the same time.
Accordingly, in cases where these flags are changed to TRUE only to restart a communica-
tions port by using an Out instruction or another instruction, change these flags to TRUE
without changing the System Settings of the device variable for CJ-series Unit.
List of System-defined Variables (** within the system-defined variable is the Unit number)
These variables are used for data exchange from the CPU Unit to the Serial Communications Unit
[output].
These variables are not available in the Modbus-RTU Slave Mode.
7-2-2 System-defined Variable
System-defined
variable
Type R/W Name Function
_CJB_SCU**P1ChgSta BOOL RW Serial Com-
munications
Unit ** Port 1
Settings
Changing
Flags TRUE: Port 1 Serial Communications Port
Settings Change
FALSE: All other statuses
Default: FALSE
_CJB_SCU**P2ChgSta BOOL RW Serial Com-
munications
Unit ** Port2
Settings
Changing
Flags TRUE: Port 2 Serial Communications Port
Settings Change
FALSE: All other statuses
Default: FALSE
7-2-3 Device Variable for CJ-series Unit for Software Switches