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Configuring the Island Bus
34
890USE19600 April 2004
Island Fallback Scenarios
Introduction In the event of a communications failure on the island or between the island and the
fieldbus, output data is put into a predefined fallback state so that the module’s
values are known when the system recovers from the failure.
When you use a basic NIM, you cannot change the fallback parameters of any
modules in the segment. All output channels on the modules go to a predefined
fallback value of 0.
Fallback
Scenarios
There are several scenarios in which Advantys STB output modules go into their
fallback states:
loss of fieldbus communications—Communications with the fieldbus master are
lost.
loss of island bus communications—There is an internal island bus
communications error, indicated by a missing heartbeat message from either the
NIM or a module.
change of operating state—The NIM may command the island I/O modules to
switch from a running to a non-running (stopped or reset) state.
In all of these fallback scenarios, the NIM disables the heartbeat message.
Heartbeat
Message
The Advantys STB system relies on a heartbeat message to ensure the integrity and
continuity of communications between the NIM and the island modules. The health
of island modules and the overall integrity of the Advantys STB system are
monitored through the transmission and reception of these periodic island bus
messages.
Because island I/O modules are configured to monitor the NIM’s heartbeat
message, output modules will go into their fallback states if they do not receive a
heartbeat message from the NIM within the defined interval.
Note: If a module fails, it needs to be replaced. The module may not go to its
fallback state.