Rockwell Automation 1785-CHBM ControlNet PLC-5 Hot Backup System User Manual - Manual (Page 47)

Publication 1785-UM024B-EN-P - January 2003
Installing and Configuring Your ControlNet PLC-5 Backup System 3-21
You can change the operational mode from the Configure tab of the
ControlNet Hot Backup screen:.
Note: When you choose Synchronous mode, you will have to enter a
Maximum Program Scan Time as well. Before selecting Synchronous
mode, enter a value into the Max Program Scan Time field. This value
should be slightly larger than the maximum program scan time
recorded in the Processor Status file. (Refer to Appendix D for more
information on program synchronization.)
To change operational mode, click on the Operational Mode box and
choose the mode you would like to use (default is Asynchronous.)
Equivalence Checks
You can perform equivalence checking to verify that selected areas in
both the primary and secondary PLC processors are identical.
You can enable various equivalence checks from the Configuration
tab of the ControlNet Hot Backup screen. Simply check the boxes
corresponding to the equivalence checks you wish to enable.
Equivalence status is updated constantly on both PLC processors
while there is a qualified backup system. If there are differences
between the two processors, a status message appears, indicating the
difference(s), and warning you that the secondary will major fault
upon switching out of Run mode and back into Run mode.
A qualified system will not major fault if an equivalence check
mismatch is detected and enabled. Only when a PLC-5 qualifies does
an equivalence mismatch cause a major fault. The Configure tab
provides you with the current status for each equivalence check;
IMPORTANT
In Synchronous mode, if there is more than one
MCP, you must select Skip I/O Update for each of
the MCPs.