5.1.7 Change of State, COS
The event controlled operation mode is used to minimize network traffic. Messages are transmitted only if a defined state or
value has changed. The condition for triggering a COS message, is determined by the insertion of COS-filters (12-38 COS
Filter), for each bit in the different PCD-words.
The filter acts like a logical AND-function: If a bit in the filter is set to “1”, the COS-function triggers when there is a change
to the corresponding bit for the PCD-word.
Parameter 12-38 COS Filter can be used to filter out undesired events for COS. If a filter bit is set to 0, the corresponding I/0
Instance bit will be unable to produce a COS message. By default, all bits in the COS filters are set to 0.
In order to signal that the connection has not been interrupted, or the device is not powered off, a Heartbeat Message is
transmitted within a specified time interval (Heartbeat Interval). This interval is defined in Attribute Heartbeat Time of the
connection object, Class 0x01.
To prevent the device from producing heavy network traffic when a value changes frequently, a Production Inhibit Time is
defined in 12-37 COS Inhibit Timer. This parameter defines the minimum time between two COS messages. If 12-37 COS
Inhibit Timer is set to 0, the Production Inhibit Timer is disabled.
Illustration 5.1 shows the different PCDs and their corresponding filter parameters.
How to Control MCA 121 EtherNet/IP
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