Specifications

Advanced Configuration Features
234
EIO0000000051 6/2010
Island Fallback Scenarios
Introduction
In the event of a communications interruption on the island or between the island
and the fieldbus, output data is put into a fallback state. In this state, output data is
replaced with pre-configured fallback values. This makes known the module’s
output data values when the system recovers from this condition.
Fallback Scenarios
There are several scenarios in which Advantys STB output modules go into their
fallback states:
z loss of fieldbus communications: Communications with the PLC are lost.
z loss of island bus communications: There is an internal island bus
communications interruption, indicated by a missing heartbeat message from
either the NIM or a module.
z 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.
z missing or non-operating mandatory module: The NIM detects this condition for
a mandatory island module.
NOTE: If a mandatory (or any other) module is not operating, it needs to be
replaced. The module itself does not go into its fallback 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 verify 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 go into their fallback states if they do not receive a
heartbeat message from the NIM within the defined interval.
Fallback States for Reflex Functions
Only an output module channel to which the result of a reflex action (see page 230)
has been mapped can operate in the absence of the NIM’s heartbeat message.
When modules that provide input for reflex functionality are not operating or are
removed from the island, the channels that hold the result of those reflex actions go
into their fallback states.