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

40-12 Industrial Communication Systems
AR
PROFINET
IOcontroller
PROFINET
IOdevice
IO Data CR
- Process data
Alarm CR
- Real-time alarm
Record data CR
- Configuration
- Parametrization
FIGURE 40.4
relations.”
Data communication in PROFINET IO is encapsulated in “application and communication
information to the context management; starting the exchange of the neighborhood information;
address resolution on the side of the IO controller; establishment of communication between IO controller
and IO device; parameterizing the submodules in the device (write records); retentive saving of
port information to the physical device (PDev); completing and checking the parameterization, and
starting the data exchange.
To establish communication between the higher level controller and an IO device, the communication
paths must be established. These are set up by the IO controller during system startup based on the
configuration data in the engineering system. This specifies the data exchange explicitly. As shown in
Figure 40.4, every data exchange has an embedded “application relation” (AR). This establishes a precisely
specified application (connection), i.e., the AR, between the higher level controller (IO controller
or IO supervisor) and the IO device. Within the AR, “communication relations” (CR) specify the data
explicitly. An IO device can have multiple ARs established from various IO controllers.
The IO controller initiates setup of an AR during system power-up. As a result, all data for the device
modeling, including the general communication parameters, are downloaded to the IO device. At the
same time, the communication channels for cyclic/acyclic data exchange (IO data CR, record data CR),
alarms (alarm CR), and multicast communication relations (MCR) are set up. CR for data exchange must
be set up within an AR. These specify the explicit communication channel between a consumer and a
provider.
40.4.4 Neighborhood and Topology Detection
PROFINET specification describes a method to replace a device without using an engineering tool.
This task is done by means of neighborhood detection with the link layer discovery protocol (LLDP)
according to IEEE 802.1 AB. This requires the ability to determine the data of neighboring devices
on a port-by-port basis using LLDP services and to provide these data to the higher level controller.
Together, these conditions enable modeling of a plant topology and convenient plant diagnostics as
well as device replacement without additional tools. PROFINET IO field devices exchange existing
addressing information with connected neighbor devices over each switch port. The neighbor devices
are thereby unambiguously identified and their physical location is determined. The LLDP protocol is
implemented in software and therefore requires no special hardware support. LLDP is independent of
the network structure (line, star, etc.). Automation systems can be configured with a line, star, or tree
structure. For this reason, it is important to know which field devices are connected to which switch
port and the identity of the respective port neighbor. The higher level controller can then reproduce the
plant topology accordingly. In addition, if a field device fails, it is possible to check whether the replacement
device has been reconnected in the proper position.
© 2011 by Taylor and Francis Group, LLC