Omron NX Series Hardware User Manual page 26

Precautions for Safe Use
External communications are also not performed during startup.
• Configure the external circuits so that the power supply to the control system turns ON only after the
power supply to the Controller has turned ON. If the power supply to the Controller is turned ON
after the control power supply, temporary errors may result in incorrect control system signals be-
cause the output terminals on Output Units may momentarily turn ON when power supply is turned
ON to the Controller.
• If you transfer data from a backup file on an SD Memory Card to the Controller when the power sup-
ply is turned ON, properly select the data groups to transfer. If the data for an unintended data group
is transferred to the Controller, it may cause the equipment to operate unpredictably.
• You cannot obtain normal input data from NX Units while the Units are restarting. Use the system-
defined variables or device variables for the NX Units on the CPU Unit in the user program to check
the validity of the I/O data before you attempt control operations.
Actual Operation
• If you change the fail-soft operation setting, the output status when the error occurs may also
change. Confirm safety before you change the setting.
• If you use fail-soft operation, write programming to determine whether Unit I/O data is valid. Without
such programming, the user program cannot distinguish between Units for which I/O refreshing is
continued and Units for which I/O refreshing is stopped.
Turning OFF the Power Supply
• Never turn OFF the power supply to the Controller when the BUSY indicator is flashing. While the
BUSY indicator is lit, the user program and settings in the CPU Unit are being backed up in the built-
in non-volatile memory. This data will not be backed up correctly if the power supply is turned OFF.
Also, a major fault level Controller error will occur the next time you start operation, and operation
will stop.
• Do not turn OFF the power supply or remove the SD Memory Card while SD Memory Card access
is in progress (i.e., while the SD BUSY indicator flashes). Data may become corrupted, and the
Controller will not operate correctly if it uses corrupted data. To remove the SD Memory Card from
the CPU Unit while the power supply is ON, press the SD Memory Card power supply switch and
wait for the SD BUSY indicator and SD PWR indicator to turn OFF before you remove the SD Mem-
ory Card.
• If the Unit power supply is turned OFF before the I/O power supply for the control system is turned
OFF, the output terminals of Output Units may malfunction and the control system may perform in-
correct output temporarily. To avoid this problem, configure the external circuit to make sure that the
Unit power supply is turned OFF only after the power supply for the control system is turned OFF.
• Do not disconnect the cable or turn OFF the power supply to the Controller when downloading data
or the user program from Support Software.
• Always turn OFF the power supply to the Controller before you attempt any of the following.
a) Mounting or removing the Units
b) Assembling the Units
c) Setting DIP switches or rotary switches
d) Connecting cables or wiring the system
e) Connecting or disconnecting the terminal blocks or connectors
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NX-series NX502 CPU Unit Hardware User's Manual (W629)