Rockwell Automation PLC-5 Fieldbus Solutions for Integrated Architecture User Manual - Manual (Page 16)

Publication 1757-UM006A-EN-P - May 2002
1-2 The Fieldbus Communication Model
Comparisons among “fieldbus technologies” typically reduces to
comparisons of data rates, message length, number of devices on a
segment, etc. These are all important communications issues and each
technology represents a particular set of trade-offs which adapt it to its
original application, and each is rooted in the technology that was
available or in vogue at the time of its development.
Using a strategy exactly opposite of FOUNDATION fieldbus, these
various communications technologies minimize dependence on local
intelligence in deference to minimum device cost, and maximize
reliance on a centralized control architecture. Measurement
instruments in such structures communicate to a central computing
system at the request of that central system. A proprietary control
application, running on the central system processes the field data and
distributes control signals to other devices back in the field.
Regardless of how open the communication scheme may be, the
control application is always proprietary.
The key distinctions between these technologies and FOUNDATION
fieldbus are; FOUNDATION fieldbus provides an open specification
for both communications and the control application. FOUNDATION
fieldbus distributes control functionality across the bus, making
maximum use of local intelligence to improve performance and
reduce total system cost. Devices are required to be interoperable,
providing the user with tools to implement a control system with
products from multiple manufacturers without custom programming.
With FOUNDATION fieldbus, the network is the control system.