Allen-Bradley ControlNet PLC-5 User Manual page 48

B-6 Backup States
Qˆiyvph‡v‚Ã &'$%$!#ÃAri…ˆh…’Ã
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 10-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.
There are, however, two cases where the PLC-5 system waits 10
seconds before starting qualification. The first case is when a
reconfiguration of the ControlNet channel occurs. When this
occurs, all connections are terminated and must be reestablished;
the 10-second wait allows the connection to be reestablished with
the partner PLC-5 processor. Note that at powerup, a ControlNet
channel reconfiguration occurs.
The second case in which the PLC-5 system waits 10 seconds
before starting qualification is when the first connection is
established on the ControlNet channel. This is indicated when
the ControlNet I/O LED changes from red to green. This could
occur, for example, when a disconnected cable gets reattached.
There is no visual indication when a qualification connection
delay is active.
• 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