Installation guide

22 Introducing the Modbus Plus Network
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1.7 Error Checking and Recovery
When a node sends a data message, it expects an immediate
acknowledgment of receipt by the destination. If none is received, the
node will attempt up to two retries of the message. If the final retry is
unsuccessful, the node sets an error which can be sensed by the
application program.
If a node detects a valid transmission from another node using the
same address, the node becomes silent and sets an error which can be
sensed by the application. The node will remain silent as long as the
duplicate node continues to participate in the token rotation. If two
devices have been inadvertently assigned the same address, the
application program can detect the duplication and handle it while the
rest of the application continues.
When a node transmits the token, it monitors the network for new
activity from its successor. If the node detects no valid activity, it
makes one retry to pass the token. If no activity is detected after the
retry, the node remains silent. This causes the network to be initialized
and a new token sequence to be created.