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Closing the control loop over the bus
Rapid Cyclical transmission with PPO using DP
Parameter up-/downloads can be achieved by using
the so-called Parameter / Process Objects - PPOs -
of 12, 20 or 28 bytes length as specified in the VDI/
VDE 3689 profile, see drawing page 16.
This procedure, however, occupies 8 bytes additional
I/O memory space in the PLC bytes per slave, and
slows down the system (see also "Timing" page 15).
Control of the drives during normal operation is often
very time critical, but it involves very few data, such
as control commands and speed reference. DP is
optimized for fast cyclical communication.
14
FCM 300 PROFIBUS / VLT 2800 PROFIBUS
Closing the control loop outside the fieldbus
for extremely fast feed-back
Features and services supported by FC motor
and the VLT 2800
Features available as described by the unit
classification
The unit classification as layed out in the PROFIBUS
Profile for VSDs describes the functionality of the unit.
There are 4 classes where class 1 signifies the lowest
performance class, and class 4 the highest.
The FC motor / VLT 2800 is a class 3 unit except for
the following features:
-
Fault buffer
-
Change access rights for parameter write
-
Change access rights for process control
-
Time difference
-
Hardware configuration ident.
The FC motor / VLT 2800 complies with the following
class 4 features:
-
Baudrate > 500 kBaud
-
Programmable content of PCD 3 through 6 (10) of
the PPO's
-
PPO type 5
MG.90.A2.02 – VLT is a registered Danfoss trademark
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