GE Industrial Solutions AF-650 GP DeviceNet - Manual (Page 16)

4 How to Control the Frequency Converter
4.1 DeviceNet Process Control Modes
This section describes two of three possible process control modes: Polling and Change of State (COS).
The third drive control mode uses the acyclical mode Explicit Messaging via the Standard DeviceNet Control Supervisory object CLASS 29H. The Control Supervisory
object is described within the DeviceNet Object Classes section, How to Access the Parameters chapter.
4.1.1 Polling
This is a classical Master-Slave connection and the standard DeviceNet op-
eration mode. The master controls the data exchange by sending cyclical
poll-requests to the connected slaves, and the slaves answers by sending a
poll-response to the master. The master can control and monitor the fre-
quency converter by polling the DeviceNet or GE drive objects (I/O Instances).
POLLED I/O
Master → slave CTW MRV
Slave → master STW MAV
4.1.2 Change of State, COS
This an event-controlled operation 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 (par. DN-20 COS Filter 1 to par. DN-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 upon a change to the corresponding bit for the PCD-
word.
The figure below shows the different PCDs and their corresponding filter parameters.
par. DN-20 COS Filter 1 to par. DN-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/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 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 two COS messages.
AF-600FP /650 GP DeviceNet Operating Instructions
15
4