Page 877 - Mechatronics with Experiments

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MATLAB , SIMULINK , STATEFLOW, AND AUTO-CODE GENERATION 863
History Exclusive (OR) state
junction
Connective Default transition
junction Transition

StateA
Default_transition
StateA2
StateA1 H
StateA2a
StateA1c
StateA1a
TransitionA1_A2
(Condition 1)
(Condition 1){func1()}func2() StateA2b
TransitionA1a_A1b
TransitionA2_A1
StateA1b

Transition label Condition Condition Transition Parallel (AND) state
action action
FIGURE A.37: Graphical components of a Stateflow diagram: state (parallel and exclusive),
transitions (normal transitions, default transitions), actions, junctions (connective and history
types), conditions.

executed. After that, the actions in the “during:” block are executed during the following
sampling periods. When a transition occurs from the currently active state, then the actions
in the “exit:” block are executed before the program transitions to another state. Multiple
“on_EventName” blocks can be defined. This allows us to define a unique set of actions
for each event.
In addition to actions, we may need to define data variables (local or persistent) in
each state to keep track of data. It is also possible that we only need the input and output
data, and no local (or persistent) data may be needed.
Step 4: Define the Transitions Between States. So far we have defined a state
hierarchy and actions within those states. We also need to define the logic to make the
transitions between those states.
Transitions are the logical flow paths between different states. To simplify the logic, it is
advisable to exercise modular programming practice and plan transitions between states
at the same hierarchy level. Otherwise, the transition logic may look like a “spaghetti
code” which means it is difficult to understand and maintain. Each transition may have a
condition which must be TRUE for the transition to occur, and an action that is executed
during the transition before the control is passed to the next state. These transition conditions
and actions are expressed with a notation on the transition path in text format. At every
hierarchy of states, there should be a default transition defined. This transition would
be used in case of ambiguity over which state to activate. This often happens on start-up
conditions. For every level of exclusive OR-states, there should be a default transition