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

Communication Aspects of IEC 61499 Architecture 55-7
FIGURE 55.4
ECC of the FB-type LIGHTS.
55.3 Logic Encapsulated in Basic FB
Let us consider in more detail how the logic is programmed in FBs. We use as example the basic FB-type
LIGHTS that encapsulates the behavioral logic of a single four-lamp LED section.
According to IEC 61499, basic FBs are defined by their interface (i.e., input and output event and data
variables), internal variables, algorithms, and a state machine called execution control chart (ECC).
Figure 55.4 shows the ECC of the LIGHTS FB as seen in FBDK. In the left pane, one sees also the list of
eight algorithms (INIT, …, SET_4, SET_1).
The algorithms are invoked in the actions associated with the states of ECC. Initially, ECC is in a
specifically designated start state; in our case this is WAIT state in the middle. For example, in the case
of INIT input event, the ECC will “jump” into state INIT, execute the first action, consisting in calling
algorithm with name INIT, then execute the second action, consisting in calling algorithm CLEAR and
emitting of output event INITO, and then will return to the WAIT state.
Algorithms can be programmed in different programming languages. For example, it is expected that
the PLC programming languages of IEC 61331-3 standard [19] may be used, among others.
55.4 Extension
Now let us consider one possible functional extension of our sample system that justifies the distribution
of the application across several computing devices. Assume that in addition to the previously considered
configuration in Figure 55.2, we add two buttons for increasing/decreasing the speed of the moving light,
a numeric display indicating the current frequency of the light update, and, most importantly, one more
section of LEDs, so the lights will “jump” from one LED section to another, as shown in Figure 55.5.
© 2011 by Taylor and Francis Group, LLC