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

41-8 Industrial Communication Systems
files (XIF) define the logical interface of the node that means the function blocks and their network
variables and configuration properties. These interface files are used later by system integration tools
for configuration and network variable binding.
Since the Neuron Chip does not support interrupts, the events and conditions of the tasks have to
be checked periodically by a scheduler. The sequence of checks depends on the priority of the tasks. In
each scheduler loop, all priority tasks are checked first. If none of these has to be processed, one of the
non-priority tasks will be checked and processed if necessary. The other remaining non-priority tasks
are checked at the end of the next loops, one in each loop. The scheduler jumps to the head of the
non-priority task list again, when the tail is reached.
41.5 Function Block-Based Design and System Integration
The function block-based design and the system integration shall be explained with the example of a
single-room sunblind control, which should realize an antiglare functionality. Such a room control
typically consists of the following functions:
• Antiglare control
The antiglare function controls the position of the sunblind and the angle of the sunblind’s lamellas
to prevent the glaring of persons, which are present in the room. A measurement of the current glare
is the luminance level in the room. As soon as the luminance exceeds a certain threshold, the sunblinds
will move down. If there is nobody in the room, the antiglare function will be switched off.
• Sunblind actuator
The sunblind actuator drives the motor of the sunblind. It receives the actuating values from the
antiglare control function.
• Luminance sensor
The luminance sensor measures the current luminance level in the room in lux.
• Occupancy sensor
The occupancy sensor detects whether a person is within the room or not. Based on this information,
it activates or deactivates the antiglare controller.
• Manual control
The position of the sunblind can be set manually using a sunblind switch, which overrides the
antiglare control. Additionally, the building management system can override the position, for
example, in the night or in case of fire.
As defined above, network variables are basic communication objects to exchange values over the network.
To separate specific automation functions and their related network variables within a node, the
application of a node is subdivided into functional blocks [11]. Figure 41.4 shows the functional block of
the sunblind controller, which realizes the antiglare functionality and, bound to this, the other needed
functional blocks. These are the sunblind switch for the manual control, the light sensor for measuring the
luminance, the occupancy sensor for the presence detection, and the sunblind actuator, which drives the
sunblind. Functional blocks define an interface, which consists of input (nvi…) and output (nvo…) network
variables and configuration properties. Configuration properties can be implemented as configuration
network variables or as properties in configuration files. Configuration network variables (nci…) can be
altered by other LonWorks devices using standard network variable propagation, but their size and count is
limited. Properties in configuration files have no such limitations, but they can only be set by network tools.
Bindings are not restricted to one-to-one interconnections. They are allowed to be of kind one-to-n
and n-to-one, too. One-to-n bindings are used if more than one input variable needs the value of one
output variable. N-to-one bindings, however, can be problematical since the input variable receives
values from different outputs, which can overwrite each other concurrently.
To ensure the interoperability among the LonWorks nodes, especially if they are from different manufacturers,
their functions and their communication interfaces have to be standardized. Therefore, the
© 2011 by Taylor and Francis Group, LLC