Profibus DP V1 for two different purposes
Fieldbus systems are used for two very different purposes with two very different sets of essentials in modern automation applications. One is transfer
of signals referring to the process itself, the other service, commissioning and set-up communication.
Transfer of control and status signals between sensors and actuators is time critical and must be processed reliably and in real time. This is accomplished
by cyclic communication where each node in the network is polled within each cycle, and each cycle has a pre-defined time. It is necessary to pre-define
and minimise the extent of data in each telegram to make this work reliably and as fast as possible.
This consideration contradicts the second use of the fieldbus, namely as a timesaving set-up and diagnostics bus. Set-up and diagnostics are not time-
critical, not continuously used, and require a larger amount of data in each telegram. Furthermore, you would tend to control this information from a PC
or an interface device (HMI) - and not from the master (typically a PLC) that controls the cyclic communication. Standard Profibus does not support
networks with several masters so set-up and diagnostics information must be contained in the standard telegram handled by the master, making for very
long and time consuming telegrams with room for information only sporadically used.
Profibus DP V1 now combines the two sets of requirements from above in a single fieldbus system, allowing a second master to use the entire network
in a specified time slot in each cycle. Profibus DP V1 thus operates with two classes of masters. Masterclass 1 (typically a PLC) performs the cyclic
communication. Masterclass 2, typically an interface device (HMI or PC), transfers non-time critical information through non-cyclic communication.
Masterclass 2 masters can be connected anywhere on the Profibus net and the communication channel can be opened and closed anytime without
disturbing the cyclic communication. You can have non-cyclic communication even without cyclic communication to for instance transfer complete pro-
grams or set-ups.
Profibus DP V1 is fully compatible with prior versions of Profibus DP V0. Profibus DP V0 and Profibus DP V1 nodes can be combined in the same network,
although the master must support Masterclass 2 communication.
User benefits:
•
Connection to the motor controls is possible from every part of the network
•
Existing network can be used for commissioning, set-up and diagnostic without disturbing of the cyclic communication
•
Both DP V1 and DP V0-nodes can be connected in the same network
•
No need for extensive telegrams in the PLC or IPC. A second master who supports DP V1 can handle set-up tasks
NB!
DP V1 is only possible for Master communication-cards which support Masterclass 2 specification.
VLT
®
Decentral FCD 300 Design Guide
1 The Decentral Concept
MG.90.S1.02 - VLT
®
is a registered Danfoss trademark
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