Omron CJ1W-ECT21 Operation Manual page 20

Precautions for Safe Use
Battery Backup
• The user program and initial values for the variables are stored in non-volatile memory in the CPU
Unit. The present values of variables with the Retain attribute and the values of the Holding, DM, and
EM Areas in the memory used for CJ-series Units are backed up by a Battery. If the Battery is not
connected or the Battery is exhausted, the CPU Unit detects a Battery-backup Memory Check Error.
If that error is detected, variables with a Retain attribute are set to their initial values and the Holding,
DM, and EM Areas in memory used for CJ-series Units are cleared to all zeros. Perform thorough
verifications and provide sufficient measures to ensure that the devices perform safe operation for
the initial values of the variables with Retain attributes and the resulting operation.
Debugging
• Forced refreshing ignores the results of user program execution and refreshes I/O with the specified
values. If forced refreshing is used for inputs for which I/O refreshing is not supported, the inputs will
first take the specified values, but they will then be overwritten by the user program. This operation
differs from the force-set/reset functionality of the CJ-series PLCs.
• You cannot upload or download information for forced refreshing with the Sysmac Studio. After down-
loading data that contains forced refreshing, change to RUN mode and then use the Sysmac Studio
to perform the operation for forced refreshing.
Depending on the difference in the forced status, the control system may operate unexpectedly.
• Do not specify the same address for the AT specification for more than one variable.
Doing so would allow the same entity to be accessed with different variable names, which would
make the user program more difficult to understand and possibly cause programming mistakes.
General Communications
When you use data link communications, check the error information that is given in _ErrSta (Controller
Error Status) to make sure that no error has occurred in the source device. Create a user program that
uses reception data only when there is no error in the source device. If there is an error in the source
device, the data for the data link may contain incorrect values.
EtherCAT Communications
• Make sure that the communications distance, number of nodes connected, and method of connec-
tion for EtherCAT are within specifications.
• Do not connect EtherCAT communications to EtherNet/IP, a standard in-house LAN, or other net-
works. An overload may cause the network to fail or malfunction.
• The maximum length between nodes is 100 m. However, some cables are specified for less than 100
m. Generally speaking, if the conductors are twisted wire rather than solid wire, transmission perfor-
mance will be lower, and reliable communications may not be possible at 100 m. Confirm details with
the cable manufacturer.
• After you transfer the user program, the CPU Unit is restarted and communications with the Ether-
CAT slaves are cut off. During that period, the slave outputs behave according to the slave settings.
The time that communications are cut off depends on the EtherCAT network configuration. Before
you transfer the user program, confirm that the system will not be adversely affected.
• If noise occurs or an EtherCAT slave is disconnected from the network, any current communications
frames may be lost. If frames are lost, slave I/O data is not communicated, and unintended operation
may occur. The slave outputs will behave according to the slave specifications. Confirm that the sys-
tem will not be adversely affected before you disconnect a slave.
• When an EtherCAT slave is disconnected or disabled, communications will stop and control of the
outputs will be lost not only for the disconnected slave, but for all slaves connected after it. Confirm
that the system will not be adversely affected before you disconnect or disable a slave.
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CJ-series EtherCAT Slave Units Operation Manual for NJ-series CPU Unit (W542)