CAAPE User's Manual - ALSTOM Signaling Inc.

Using CAAPE Graphics6.5. EDITING LOGIC COMPONENTSLadder logic is a graphical representation of the Vital or non-vital logic in an application.As with the older text-based logic format, its purpose is to specify the behavior of asystem - how the system responds to the various types of inputs it receives, and when itactivates or deactivates its various types of outputs. However, ladder logic has theadvantage of being a more "visual" format and represents the logic in a way that is morein keeping with traditional relay-based diagrams.Ladder logic consists of a series of statements. Which types of statements are availablein a given set of ladder logic depends on the type of application. The general editingprocess involves:• Adding Boolean equations and other types of statements and setting theirproperties.• For Boolean equations, defining the results and variables and their logical structure.• Declaring any internal variables in the logic. Internal variables are variables that donot represent physical hardware I/O or message bits, but rather internal data used inthe equations.• Defining constants when applicable. Constants are meaningful names that can beused to stand for numeric values. For example, the constant MAX_COUNT could bedefined as standing for a value of 10, and when the statement IF(COUNT