Control; Devicenet Process Control Modes - Danfoss VLT DeviceNet MCA 104 Programming Manual

Control

4 Control

4.1 DeviceNet Process Control Modes

This section describes 2 of 3 possible process control
modes:
•
Polling.
•
Change of state (COS).
The 3rd FC control mode uses the acyclic mode explicit
messaging via the standard DeviceNet control supervisory
object class 29H. The control supervisory object is
described in chapter 5.3 DeviceNet Object Classes.
4.1.2 Change of State, COS
COS is an event-controlled operating mode 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
(parameter 10-20 COS Filter 1 to parameter 10-23 COS Filter 4), 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 after a change to the corresponding bit for
the PCD word.
Illustration 4.1 Different PCDs and the Corresponding Filter Parameters
Parameter 10-20 COS Filter 1 to parameter 10-23 COS Filter 4 can be used to filter out undesired events for COS. If a filter bit is
set to 0, the corresponding I/O instance bit is unable to produce a COS message. By default, all bits in the COS filters are set
to 0.
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 code 0x05.
To prevent the device from producing heavy network traffic if a value changes frequently, the production inhibit time (an
attribute of the connection object) is defined. This parameter defines the minimum time between 2 COS messages.
MG92F102
Programming Guide
4.1.1 Polling
Table 4.1 is a classic master/slave connection and the
standard DeviceNet operating mode. The master controls
the data exchange by sending cyclic poll-requests to the
connected slave, and the slave answers by sending a poll-
response to the master. The master can control and
monitor the frequency converter by polling the DeviceNet
or Danfoss objects (I/O instances).
Master
Slave
Table 4.1 Standard DeviceNet Operation Mode - Polled I/O
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⇒
Slave
CTW
⇒
Master STW
4 4
MRV
MAV
9