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Startup Settings and Maintenance Section 6-6
!Caution If Output Unit’s external power supply goes on before the PLC’s power supply,
the Output Unit may malfunction momentarily when the PLC first goes on. To
prevent any malfunction, add an external circuit that prevents the Output
Unit’s external power supply from going on before the power supply to the
PLC itself. Create a fail-safe circuit like the one described above to ensure
that power is supplied by an external power supply only when the PLC is oper-
ating in RUN or MONITOR mode.
6-6-4 Power OFF Detection Delay Setting
Normally a power interruption will be detected about 10 to 25 ms (2 to 5 ms
for DC power supplies) after the power supply voltage drops below 85% of the
minimum rated value(80% for DC power supplies). There is a setting in the
PLC Setup (address 225 bits 0 to 7, Power OFF Detection Delay Time) that
can extend this time by up to 10 ms (up to 2 ms for DC power supplies).
When the power OFF interrupt task is enabled, it will be executed when the
power interruption is confirmed, otherwise the CPU will be reset and operation
will be stopped.
PLC Setup
When using the CX-Programmer, make the settings on the Timings Tab Page.
The following table shows the corresponding settings when using a Program-
ming Console.
6-6-5 Disabling Power OFF Interrupts
Areas of the program can be protected from power OFF interrupts so that they
will be executed before the CPU Unit even if the power supply is interrupted.
This is achieved by using the DISABLE
INTERRUPTS (DI(693)) and ENABLE INTERRUPTS (EI(694)) instructions.
This function can be used with sets of instructions that must be executed as a
group, e.g., so that execution does not start with intermediate stored data the
next time power is turned ON.
Program-
ming Con-
sole
address
Name Meaning Setting Default
+256, bits
00 to 07
Power
OFF
Detection
Delay
Set the time to
delay before
detecting a
power interrup-
tion.
00 to 0A (Hex): 0 to 10 ms 00 (Hex):
0ms
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