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

Communication Aspects of IEC 61499 Architecture 55-9
The logic and modes of operation of the new system shall remain the same. The changes to the FB
model will closely follow the changes introduced into the physical system. For each new peripheral element,
we have added a new FB. There is only one extra FB FREQ not corresponding to any physical component.
This block implements a global variable storing the current flashing frequency value.
The frequency is set by the time-setting knob and can be changed (increased or decreased) as a result
of pressing buttons “+” and “−.” The current flashing frequency value is passed to the numeric display
and to the “pulse” generator in the FB PERIODIC.
It is interesting that we did not need to change the logic at all! We just added one more FB LOGIC2
and “cascaded” it after LOGIC1. When the running light reaches the rightmost or leftmost position at
the LED block, it “jumps” to the next LED block. For that, the event output CR of one block is connected
to the event input NEW of the other.
Similar to the first version of the system, the extended system can be easily simulated by substituting
FBs interfacing physical peripheral devices by the FBs imitating this on screen.
55.5 Distribution
IEC 61499 implies a two-stage design process. First, an application is created as a network of FBs. At
this stage, communication between FBs is abstract, implemented via event and data flow arcs. Second,
the application can be distributed across several devices as illustrated in Figure 55.6. The connections
Application
FB2
Device 1
FB2
Device border
crossing points:
here Communication
Function Blocks
for inter-device
communication
are to be inserted
FB1
FB1
Device 2
FB3
FB3
Device 1
FB2
Device 2
Subscribe
FB1
Publish
Subscribe
FB3
Publish
Network
FIGURE 55.6 Distribution of the application across two devices: the connections between blocks which are mapped
to the same device are preserved. The connections crossing the device boundaries are appended by communication
FBs. (From Vyatkin, V., IEC 61499 Function Blocks for Embedded Control Systems Design, Instrumentation Society of
America, Research Triangle Park, NC, 2007.)
© 2011 by Taylor and Francis Group, LLC