Rockwell Automation 1785-CHBM ControlNet PLC-5 Hot Backup System User Manual - Manual (Page 88)

Publication 1785-UM024B-EN-P - January 2003
B-8 Backup States
• Backup configuration parameters passed to qualifying system
After the qualifying PLC-5 system has waited, if necessary, for
the qualification connection delay, the backup configuration
parameters are passed from the primary PLC-5 system to the
qualifying PLC-5 system. The backup configuration parameters
which were originally in the qualifying system are overwritten
and lost. The backup configuration parameters that are passed
from the primary system and overwritten on the qualifying
system are:
– Operational Mode
– Equivalence Checks
– Designated Primary
– Maximum Program Scan Time
– Crossload File 1
– Crossload File 2
– Crossload File Low
– Crossload File High
– Crossload over DH+ = 0
– Requalification of dual primary PLC-5s = 0
• Equivalence checks
The PLC-5 ControlNet backup system does not download the
entire memory from the primary system to the secondary
system; there are certain data table values that are crossloaded.
Areas such as the program files and data table structures may be
different between the primary and secondary system. In some
applications, this is desirable. However, in most applications,
you must know for certain whether the primary and secondary
systems are identical, or whether they may differ in certain
areas. Equivalence checking gives you the option of enforcing a
qualification major fault if the systems differ. (Refer to Chapter 4
for descriptions of specific major faults.)
You can implement qualification equivalence checking by
enabling checksum calculations for different memory areas of
the PLC-5 system. These checksums are calculated on both the
primary and qualifying secondary system, and are passed from
the primary system to the qualifying system before equivalence
checking is performed. If you enable equivalence checking for a
particular area, and the primary checksum is different than the
qualifying checksum, qualification fails and the qualifying
controller declares a major fault.