20
CP2E CPU Unit Software User’s Manual(W614)
z External Circuits
• Always configure the external circuits to turn ON power to the PLC before turning ON power to the
control system. If the PLC power supply is turned ON after the control power supply, temporary
errors may result in control system signals because the output terminals on DC Output Units and
other Units will momentarily turn ON when power is turned ON to the PLC.
• Fail-safe measures must be taken by the customer to ensure safety in the event that outputs from
output terminals remain ON as a result of internal circuit failures, which can occur in relays, tran-
sistors, and other elements.
• If the I/O Hold Bit is turned ON, the outputs from the PLC will not be turned OFF and will maintain
their previous status when the PLC is switched from RUN or MONITOR mode to PROGRAM
mode. Make sure that the external loads will not produce dangerous conditions when this occurs.
(When operation stops for a fatal error, including those produced with the FALS instruction, all out-
puts from PLC will be turned OFF and only the internal output status in the CPU Unit will be main-
tained.)
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