Allen-Bradley ControlNet PLC-5 User Manual page 53

The Qualification State Data Table crossload reads data table
values from the primary PLC-5 system and writes these values to
the qualifying PLC-5 system. The State Data Table crossload
only crossloads specific parts of the data table. There are 4
different parts of the data table that are crossloaded:
- Timer Accumulators
- Counter Accumulators
- PD elements
- User-selectable files
It may take many seconds for the Qualification State Data Table
crossload to finish. The time it takes to complete the data table
crossload primarily depends on the amount of data table data to
be crossloaded.
Even though the State Data Table crossload may take many
seconds to complete, the data that is transferred from the primary
system to the qualifying system is fresh. In other words, the
crossloaded data is not sitting in a buffer getting stale, waiting for
all the data to be crossloaded. Each packet of data is immediately
written into the qualifying system's data table. So, no matter how
long the Qualification State Data Table crossload takes, the data
table elements which are crossloaded into the qualifying system
closely match the values in the primary system.
The Qualification State Data Table crossload does not occur if the
Data Table Structures are not the same. If you want to ensure that
a Qualification State Data Table crossload occurs, you must
enable equivalence checking for the Data Table structure area.
If, for some reason, the State Data Table crossload fails,
qualification also fails and a major fault is declared for the
qualifying system.
• Transition to Secondary backup state
After the State Data Table crossload is successfully completed,
the secondary system transitions into the Secondary backup state,
and qualification is complete. The LED's on the 1785-CHBM
cartridge indicate the new backup state. Also, the Qualified LED
on the primary system turns solid green, indicating that there is a
qualified secondary system.
If you selected the Designated Primary feature, and the odd node
of the odd-even backup pair has just gone through secondary
qualification, a switchover automatically occurs. The odd node
becomes the primary system, and the even node transitions from
the primary system to the secondary system. The even node's
transition from primary to secondary happens immediately. The
even node does not go through qualification when it becomes the
secondary system.
Backup States
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