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GFK-0467K Chapter 2 System Operation 2-15
2
Clearing the Fault Table with the Key Switch
If you turn the key from the RUN to STOP and back to RUN position during the 5 seconds when
the RUN light is flashing this will cause the faults to be cleared and the CPU will be placed into
RUN mode. The light will stop flashing and will go solid ON at this point. The switch is required
to be kept in either RUN or STOP position for at least 1/2 second before switching back to the
other position.
Note
If you allow the 5 second timer to expire (RUN light stops flashing) the CPU will
remain in its original state, STOP/FAULT mode, with faults in the fault table. If
you turn the Key Switch from the STOP to RUN position again at this time, the
process will be repeated with this being the first transition.
The following table provides a summary of how the two CPU parameter settings affecting the Key
Switch (R/S Switch and IOScan-Stop) and the Key Switch’s physical position affect PLC.
R/S Key Switch
Parameter in CPU
Configuration
Key Switch
Position
IOScan-Stop
Parameter in CPU
Configuration PLC Operation
OFF X X All PLC Programmer Modes are allowed.
ON ON/RUN X All PLC Programmer Modes are allowed.
ON OFF/STOP X PLC not allowed to go to RUN.
ON Toggle Key
Switch from
OFF/STOP to
ON/RUN
X PLC goes to RUN if no fatal faults are present;
otherwise, the RUN LED blinks for 5 seconds.
ON Toggle Key
Switch from
ON/RUN to
OFF/STOP
NO PLC goes to STOP–NO IO
ON Toggle Key
Switch from
ON/RUN to
OFF/STOP
YES PLC goes to STOP–IO
X=Has no affect regardless of setting
Enhanced Memory Protect with Release 8 and Later CPUs
In the Release 8 and later CPUs, the Key Switch has all the functionality discussed above, plus, by
setting a parameter in the programming package, it can be used to protect RAM so that the RAM
cannot be changed from the programming software. Two types of operations are blocked when
this memory protection is enabled: the user program and configuration cannot be modified and the
force and override of point data is not allowed. This is activated through the Mem Protect field in
the 350 or 360 series CPUs module configuration screen in Logicmaster. The default is Disabled.