Rockwell Automation 1785-CHBM ControlNet PLC-5 Hot Backup System User Manual - Manual (Page 86)

Publication 1785-UM024B-EN-P - January 2003
B-6 Backup States
Backup State Transitions In the previous section, we described the possible states of the PLC-5
ControlNet backup system, with references to transitions between
states. For example, when in the No Control backup state, if you
change a configuration parameter to an invalid value, the PLC-5
ControlNet backup system transitions into the Invalid backup state.
This section describes two backup state transitions: Qualification and
Switchover.
Qualification
Qualification occurs when the PLC-5 ControlNet backup system
transitions from the No Control backup state to either the Secondary
backup state or the Primary backup state. You activate this backup
state transition by changing the PLC-5 system from Program mode to
Run mode.
You can tell that a qualification is active when the Qualified LED
blinks yellow and green, alternately.
Qualification: From the No Control State to the Primary State
The backup state transition from No Control backup state to the
Primary backup state occurs when the PLC-5 system transitions from
Program mode to Run mode and
• there is no partner PLC-5 system, OR
• the partner PLC-5 system is not in Primary backup state, OR
• the partner PLC-5 system is not communicating with this PLC-5
processor
The transition from No Control backup state to Primary backup state is
simple. There are no checks to be done. The transition occurs
immediately if there is no Qualification Connection Delay. Once the
transition to the Primary Backup State is complete, the LED’s on the
1785-CHBM cartridge indicate the new backup state.