Real-time fieldbus communications using Profibus networks
Tovar, E.; Vasques, F.
Industrial Electronics, IEEE Transactions on
Volume 46, Issue 6, Dec 1999 Page(s):1241 - 1251
Digital Object Identifier 10.1109/41.808018
Summary:This paper provides a comprehensive study on how to use Profibus
fieldbus networks to support real-time industrial communications, that
is, on how to ensure the transmission of real-time messages within a
maximum bound time. Profibus is base on a simplified timed token (TT)
protocol, which is a well-proved solution for real-time communication
systems. However, Profibus differs with respect to the TT protocol, thus
preventing the application of the usual TT protocol real-time analysis.
In fact, real-time solutions for networks based on the TT protocol rely
on the possibility of allocating specific bandwidth for the real-time
traffic. This means that a minimum amount of time is always available,
at each token visit, to transmit real-time messages, transversely, with
the Profibus protocol, in the worst case, only one real-time message is
processed per token visit. The authors propose two approaches to
guarantee the real-time behavior of the Profibus protocol: (1) an
unconstrained low-priority traffic profile; and (2) a constrained
low-priority traffic profile. The proposed analysis shows that the first
profile is a suitable approach for more responsive systems (tighter
deadlines), while the second allows for increased nonreal-time traffic
throughput
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