Build and Test a Function

You can build custom functions for use in the functional programming of FBD algorithms in Basic function block types. Such functions do not themselves produce compilable code; rather, they serve as templates for the production of compilable code when they are used in FBD algorithms. Start the FBEditor. Create a new function template in the editor by: Opening a file containing an existing function, for example the X2Y2_FN file in the src\student folder; or Clicking the New =>Function menu item as shown at right. Edit the function's elements: Edit the function's interface. Make sure that the function only has a single output, named OUT. Edit the function's properties. Enter package fb.rt.<mypkg>; in the Compiler Info header field, where <mypkg> is the name of the src subdirectory you are working in, for example, plc.functions. In the Compiler Info classdef field, enter a parenthesized expression in the IEC 61131-3 ST language, expressing the value of OUT in terms of the function's input variables. Each usage of an input variable name should be set off with a blank space, for instance ( IN1 + IN2 ) or (( X + Y )*( X - Y )). When your editing is complete, save your work with the Save As...=>XML dialog. It is a good idea to save your work from time to time while editing, too! You can't save this element as a Java® file - It's used as a template for code generation in FBD algorithms. Since this element doesn't generate code, it can't be tested by itself, but only as part of an FBD algorithm of a Basic FB Type. See X2Y2_FN and X2Y2_FN_FBD in the FBDK's src/student folder for an example.