User manual

Hot Standby
33002479 06 07/2008 323
Global Data
(Publish/
Subscribe)
Service
The Hot Standby primary CPU NOE is 1 station within a distribution group.
Distribution groups exchange application variables. Exchanging application
variables allows the system to coordinate all the stations in the distribution group.
Every station publishes local application variable in a distribution group for all other
stations and can subscribe to remote application variables independent of the
location of the producer.
The communication port has only 1 multicast address.
In this network service, the Modicon Quantum Hot Standby with Unity controllers are
viewed like only 1 station. The primary CPU NOE publishes the Hot Standby
application variables and receives the subscription variables. The secondary NOE
global data service is in a stopped state.
When the Hot Standby switchover occurs, the primary CPU NOE stops the global
data service. The NOE does not publish the local variable during a switchover. And
after the switchover, the new primary CPU NOE starts to publish application
variables and to receive the subscription variables.
Note:
You must account for the following Ethernet I/O scanning considerations during a
switchover.
z If MSTR/IEC function block is used for TCP/IP, only some of the opcode will be
used. Therefore, the block does not complete its transaction, and it returns error
code 0•8000.
z While the NOE is in the process of performing the transaction, a new MSTR/IEC
function block may become active.
z The output states of the scanned I/Os will follow the state defined in the last
value option configured in the I/O scanning table of the NOE module (in Unity
Pro software).
These 2 states are either:
1. set to 0
2. hold last
With the above considerations, we recommend using switchover with Ethernet I/O
scanning for less critical applications.