Schneider Electric 890USE19600 Version 1.0 manual Island Fallback Scenarios

Configuring the Island Bus

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
	There are several scenarios in which Advantys STB output modules go into their
Scenarios	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.
	Note: If a module fails, it needs to be replaced. The module may not go to its
	fallback state.
Heartbeat
	The Advantys STB system relies on a heartbeat message to ensure the integrity and
Message	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.

34 890USE19600 April 2004