Rockwell Automation 1785-CHBM ControlNet PLC-5 Hot Backup System User Manual - Manual (Page 131)

Publication 1785-UM024B-EN-P - January 2003
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switchover The transfer of control from the primary PLC-5 to a qualified
secondary PLC-5. This can occur under the following
conditions:
• When the primary goes out of Run mode, due to:
- being put in Program, Remote Program, or Remote Test mode
- a loss of power to the PLC-5
- a major fault during program execution
- a PLC-5 failure
• When you issue a command to switch over
• When operating in Synchronous or Asynchronous mode,
with the designated primary option selected, and the
designated primary PLC-5 becomes qualified
synchronous mode A mode you configure that provides program scan
synchronization between the primary and secondary PLC-5s. In
addition, the remote inputs received by both PLC-5s are
introduced into their input data tables at the same time.
This synchronous method of operation is intended to minimize
the bump in the controlled application when a PLC-5 switchover
occurs. However, to achieve this level of synchronization, the
program scan time must be configured to operate at a fixed
minimum scan time. Therefore, overall program scan rate will
not be as fast as you can achieve in Asynchronous mode. The
default setting is Asynchronous.
system operating parameters Functions of the ControlNet PLC-5 hot backup system that
determine how the overall system will operate. These include:
• Backup Operating mode
• designated primary
• Equivalence mode
• secondary qualification time delay
• automatic data crossload during qualification
These parameters are transferred from the active primary to the
secondary PLC-5 as the secondary goes through qualification.
With the exception of the designated primary parameter, all
other system operating parameters can be modified during
system operation.