GE 90-30 PLC Series Installation And Hardware Manual page 127

5
Protect your keys. Each new 350–374 CPU is supplied with a pair of keys for the key switch. If
you use one or more of the key switch protection features described above, we recommend you
carefully guard your keys. If they are lost, misplaced, or stolen, you may be locked out from
working on your PLC, and unauthorized persons may have access to it. Replacement keys can be
purchased under part number 44A736756-G01. This kit contains three sets of CPU keys. All 350–
374 CPUs use the same key.
Of course, you can choose to not use any of the keyswitch protection features, in which case you
can leave the keyswitch set to the OFF position, and leave the two configurable keyswitch features
set at their default (disabled) settings. Then, you will not need to use a key to access the PLC.
Sequential Event Recorder (SER) Instruction
This functional instruction (programmed in ladder logic) was introduced in CPU firmware release
9.0 and is available in all of the 350 – 374 CPUs that have this firmware. The purpose of the SER
is to provide a dynamic troubleshooting and debugging tool. In effect, it takes "snapshots" of the
on/off status of groups of discrete points that you specify. You also specify how many of these
snapshots to take, when and how often they will be taken, and where in memory they will be
stored. The stored snapshots can be analyzed to see the time relationship of the bits sampled.
Please see the Series 90-30 PLC CPU Instruction Set Reference Manual, GFK-0467K or later for
details on using this instruction. Some feature highlights:
5-16 Series 90-30 PLC Installation and Hardware Manual – August 2002
Run/Stop (configurable): This feature was introduced in CPU firmware release 7.0. It is, by
default, disabled. It is not functional unless the R/S Switch: parameter on the CPU
configuration screen is set to Enabled. This feature, when enabled, lets you stop the PLC by
turning the key switch to OFF, or start the PLC running by turning the key switch to ON (if
there are no faults).
If the PLC has a non-fatal fault, turning the key switch from OFF to ON will cause the RUN
light on the power supply to flash for 5 seconds. If you again turn the key switch OFF, then
ON during the 5 seconds, the fault will clear and the PLC will go into run mode (and the RUN
light will stay ON).
If the PLC has a fatal fault, you will not be able to use the keyswitch to either clear the fault
or put the PLC into run mode. You will have to correct the cause of the fault before being able
to resume operation.
RAM Memory and Override Protection (configurable): This feature was introduced in
CPU firmware release 8.0. This feature is, by default, disabled. It is not functional unless the
Mem Protect: parameter on the CPU configuration screen is set to Enabled. If this feature is
enabled and the keyswitch is ON, (1) user RAM memory cannot be changed (2) discrete points
cannot be overridden, and (3) the TOD clock cannot be changed with the Hand Held
Programmer (however, the TOD clock can still be changed using programming software).
An SER function block collects up to 32 contiguous or non-contiguous bits per sample.
Each SER function block can capture up to 1024 samples.
If the SER is embedded in a periodic subroutine, sampling rate is determined by the periodic
subroutine execution rate.
Only the trigger sample is time stamped. The trigger sample can be time-stamped in BCD
(maximum resolution of 1 s) or POSIX format (maximum resolution of 10ms). The time
GFK-0356Q