Rockwell Automation 1785-CHBM ControlNet PLC-5 Hot Backup System User Manual - Manual (Page 87)

Publication 1785-UM024B-EN-P - January 2003
Backup States B-7
Qualification: From the No Control State to the Secondary State
The backup state transition from No Control backup state to
Secondary backup state occurs when the PLC-5 system transitions
from Program mode to Run mode, and the partner PLC-5 processor is
in the Primary backup state and is communicating with this PLC-5
processor. The entire qualification process has many components:
• Connection delay
There may be up to a 13-second delay before qualification
begins because of the time needed to establish connections on
the ControlNet channel. It is important to make a connection to
the partner PLC-5 processor in order to determine if this
processor is to become primary or secondary. If the partner
PLC-5 processor is primary, this processor goes through
qualification to become a secondary system. If the partner PLC-5
processor is not the primary, or if a partner is not on the
ControlNet channel, this processor goes through qualification to
become primary. In most cases there is no qualification
connection delay.
When a reconfiguration of the ControlNet channel occurs, all
connections are terminated and must be reestablished; the
13-second wait allows the connection to be reestablished with
the partner PLC-5 processor. Note that at powerup, a ControlNet
channel reconfiguration occurs.