wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

40-2 Industrial Communication Systems
its component-based architecture, the communication in PROFINET CBA is configured rather than
programmed. On the other hand, the communication with PROFINET CBA offers bus cycle times
of approximately 50–100.ms (when the sole TCP/IP services are used), roughly compatible with RT
requirements in modular plant manufacturing. Faster bus cycles (on the order of milliseconds) are possible
if an additional data-exchange modality that also uses Ethernet frames is activated.
A more recent version of the PROFINET specifications introduced PROFINET IO (input output) in
order to deal with the more-demanding distributed I/O. PROFINET IO features RT communication (best
effort paradigm) and isochronous real-time (IRT) communication (reserved band and time paradigm)
with the distributed I/O. The designations RT and IRT are used solely to describe the RT properties of
communication within PROFINET IO; the user can scale the performance following the application
requirements. PROFINET IO describes the overall data exchange between controllers and devices as well
as the parameterization and diagnostic options. The bus cycle times for the data exchange are much faster
than in PROFINET CBA, e.g., cycle time in the order of few hundred microseconds is possible.
In the following of this chapter, PROFINET IO will be discussed in details, since it is the more innovating
part of the PROFINET concept. Currently, PRONIFET CBA is diffused and used mainly in the
North American market, while it is not well established in Europe and other continents. On the contrary,
PROFINET CBA is the optimal solution for plant supervising and control. PROFINET CBA and
PROFINET IO can be operated separately and in combination such that a PROFINET IO plant appears
in the plant view as a PROFINET CBA unit.
40.1.1 Device Classes in PROFINET IO
PROFINET follows the provider/consumer model for data exchange. The provider (i.e., the source of data
as defined by IEC Standard), usually the field device at the process level, provides process data to a consumer
(normally a PLC with a processing program). In principle, a PROFINET IO field device can contain
any arrangement of provider/consumer functions. Figure 40.1 presents the device classes (IO controller,
IO supervisor, IO device) and the communication services. The following devices classes are defined to
facilitate structuring of PROFINET IO field devices:
IO Controller: This is typically the programmable logic controller (PLC) on which the automation program
runs (corresponds to the functionality of a class 1 master in PROFIBUS).
IO Supervisor (e.g., engineering station): This can be a programming device (PG), personal computer
(PC), or human machine interface (HMI) device for commissioning or diagnostic purposes.
IO Device: An IO device is a distributed I/O field device that is connected via PROFINET IO (corresponds
to the function of a slave in PROFIBUS).
PROFINET IO-controller
Example:
A PLC that accesses
the process signal
through the process
image
IO-C
- Diagnosis
- Up-download
PROFINET IO-supervisor
IO-S
Example:
A system used for
diagnosis and
commissioning
- Configuration
- Process data
- Alarms
IO-D
Example:
A field device that
read and write I/O
Ethernet
- Diagnosis
- Parametrization
- Status/control
PROFINET IO-device
FIGURE 40.1
Device classes and their relations.
© 2011 by Taylor and Francis Group, LLC