21.2 CREATING FUNCTION BLOCKS

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When developing a complex system it is desirable to create additional function blocks. This can be done with other FBDs, or using other IEC 61131-3 program types. Figure 305 shows a divide function block created using ST. In this example the first statement declares it as a FUNCTION_BLOCK called divide. The input variables a and b, and the output variable c are declared. In the function the denominator is checked to make sure it is not 0. If not, the division will be performed, otherwise the output will be zero.

Figure 305 Function Block Equivalencies