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Using a Quantum IEC Hot Standby System
128
840 USE 106 00 January 2003
IP Address
Swapping at
Switchover
The Quantum network option module NOE 771 (Ethernet TCP/IP) supports address
swapping at switchover when used in a Hot Standby system. This behaves pretty
much like the address swap of the Modbus Plus ports, except that the offset is 1
instead of 32. So when having the NOE 771 installed with an IP address of
AAA.BBB.CCC.DDD configured, the module in the Primary rack is going to take that
one. The module in the same slot of the Standby rack takes address
AAA.BBB.CCC.(DDD+1). In case DDD = 254, (DDD+1) is going to be 1, and at
switchover the modules exchange their IP addresses. The address swap feature of
the NOE 771 cannot be controlled, it is always activated.
Nontransfer Area
of State RAM
Although customizing transfers is not an option, you should designate a block of 4x
registers as the nontransfer area. These registers are ignored when state RAM
values are transferred from the Primary controller to the Standby. Placing registers
in the nontransfer area is one way to reduce scan time because the Primary PLC to
CHS transfer time is shorter. See
State RAM, p. 129
for more detail.
Note: The Quantum Hot Standby system swaps Modbus Plus addresses almost
instantaneously at switchover. This means that host devices which are polling the
Quantum controller can be assured that they are always talking to the Primary
controller and that the network has no downtime during switchover.
Note: NOE 771 XX is the only Ethernet option module that supports the IP address
swap, all other NOEs will take the IP address that’s being configured for them, no
matter if they reside in the Standby or Primary rack.
NOE 771 XX modules must be configured in the same slot of the Primary and
Standby Backplanes.
NOE 771 XX requires minimum firmware revision 1.10 or higher.
Note: Even if the built in I/O-Scanner of the NOE 771 00 module is used for data
exchange or I/O modules, this mechanism does not provide full uninterrupted
communication in case of a switchover. Some connection losses may occur and/
or some non-actual data may be provided by the I/O-Scanner. Therefore,
Schneider Electric does not recommend applying this feature for I/O serving.