Queuing Of Process Data Updates - ABB COM600 Station Automation Series User Manual

1MRS756125
2.3.10.
COM600 Station Automation Series
User's Guide
Switch Fault Tolerance
The Switch Fault Tolerance feature of the Intel network adapter requires the Teaming
Feature be enabled.

Queuing of Process Data Updates

This section describes the common queue mechanism for OPC Clients (slave protocols)
in COM610/615. There might be additional queuing mechanisms on different levels of
the protocol stacks, that are specific for the protocol, which are not described here.
Process data updates are mainly queued in the OPC Clients of the COM610/615. Each
OPC Client has its own queues independent from other clients, which prevents disturb-
ances on one client connection from interfering with other connections. There are four
separate queues for different type of data with configurable length.
• High Priority
•
command replies/confirms
•
internal protocol stack control commands
•
protocol stack database initialization commands
• State Indications
• binary data and other state indications
• Measurements
• analog data
• Interrogated
• interrogation related data and commands
Queue logic
For high priority and interrogated queues the oldest message is skipped when the queues
fill up. Generally these queues should never fill up since they contain a limited number
of updates (proportional to the number of OPC items).
When the state indication queue is full, the new updates are always skipped until there
is free space in the queue.
When the measurement queue is full, an older update is always skipped when a new
update is pushed on the queue.
The updates are skipped according to the following logic:
• If an item has two or more updates, the oldest update is skipped
• If no item has two or more updates, the oldest update in the queue is skipped.
For measurements, older updates for an item are also skipped when the queue reaches
a configurable percent of the maximum capacity (but only if there is an item with multiple
outstanding updates to send).
COM600 3.2
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