Mitsubishi Electric RJ71PB91V-U-IN-E User Manual page 4

[Design Precautions]
WARNING
● When connecting an external device with a CPU module or intelligent function module to modify data
of a running programmable controller, configure an interlock circuit in the program to ensure that the
entire system will always operate safely. For other forms of control (such as program modification,
parameter change, forced output, or operating status change) of a running programmable controller,
read the relevant manuals carefully and ensure that the operation is safe before proceeding. Improper
operation may damage machines or cause accidents.
● Especially, when a remote programmable controller is controlled by an external device, immediate
action cannot be taken if a problem occurs in the programmable controller due to a communication
failure. To prevent this, configure an interlock circuit in the program, and determine corrective actions
to be taken between the external device and CPU module in case of a communication failure.
● Do not write any data to the "system area" and "write-protect area" of the buffer memory in the
module. Also, do not use any "use prohibited" signals as an output signal from the CPU module to
each module. Doing so may cause malfunction of the programmable controller system. For the
"system area", "write-protect area", and the "use prohibited" signals, refer to the user's manual for the
module used.
● If a communication cable is disconnected, the network may be unstable, resulting in a communication
failure of multiple stations. Configure an interlock circuit in the program to ensure that the entire
system will always operate safely even if communications fail. Failure to do so may result in an
accident due to an incorrect output or malfunction.
● To maintain the safety of the programmable controller system against unauthorized access from
external devices via the network, take appropriate measures. To maintain the safety against
unauthorized access via the Internet, take measures such as installing a firewall.
● When a communication error occurs on the PROFIBUS-DP network, the operating status of each
station is as shown below ((1), (2), or (3)). Check the communication status information ('Diagnostic
information detection signal' (X1), 'Diagnostic information area (for mode 3)' (Un\G23072 to
Un\G23321), and 'Extended diagnostic information area (for mode 3)' (Un\G23328 to Un\G23454))
and configure an interlock circuit in the program to ensure that the entire system will operate safely.
Failure to do so may result in an accident due to an incorrect output or malfunction.
(1) The DP-Master holds the input data before a communication error occurs.
(2) When the DP-Master has gone down, the output status of each DP-Slave is dependent on the
parameter setting.
(3) When a DP-Slave has gone down, the output status of other DP-Slaves is dependent on the
parameter setting of the DP-Master.
● When a stop error has occurred in the CPU module, the status of the RJ71PB91V is as shown below.
(1) When "Output Mode upon CPU Error" is set to "Clear".
• Data exchanges with DP-Slaves are interrupted.
• Output data in the buffer memory of the RJ71PB91V are cleared and are not transmitted.
• Input data received from DP-Slaves when a stop error has occurred in the CPU module are
held in the buffer memory of the RJ71PB91V.
(2) When "Output Mode upon CPU Error" is set to "Hold".
• Data exchanges with DP-Slaves are continued.
• Output data in the buffer memory of the RJ71PB91V are held the value when a stop error has
occurred in the CPU module and are transmitted to DP-Slaves.
• The buffer memory of the RJ71PB91V is updated by input data received from DP-Slaves.
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