Rockwell Automation 1785-CHBM ControlNet PLC-5 Hot Backup System User Manual - Manual (Page 93)

Publication 1785-UM024B-EN-P - January 2003
Backup States B-13
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 - unless there is a delay.
There are three reasons why there may be a delay in
transitioning to secondary backup state:
– if you set word 39 (completion of qualification)
– all scheduled connections have not been attempted yet (to
shorten the delay, you should inhibit unconnected devices to
reduce qualification time). All scheduled connections will be
attempted at least once to make sure the secondary PLC-5 has
all the same connections as the primary PLC-5.
– if you set word 13 (qualification delay)
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.