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28. FUNCTION BLOCK PROGRAMMING

• This is a procedural programming language that resembles block diagrams. To date this has been primarily popularized by programs such as Labview.

28.1 INTRODUCTION

•This graphical language is part of the IEC 1131-3 standard.

•An example is given below.

N7:0 SIN

*

A < B

O:000/01

N7:1

LN

N7:2

•There are different data types for the connection lines.

•Inputs and outputs can be negated by adding a inverting input or output.

• The functions in the diagrams are based on the other functions available. The inputs to a function enter on the left of the block, and the outputs of the function emerge from the right.

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Structural Text Function	Function Block Equivalent
	A				O
O := ADD(A, B);			ADD
	B

• Some functions can have a variable number of arguments. Here there is a third value input to the add block. This is known as overloading.

Structural Text Function	Function Block Equivalent
	A				O
O := ADD(A, B, C);			ADD
	B
	C

• The ADD function in the example must always have the same inputs, other functions may have variable numbers of arguments.

Structural Text Function	Function Block Equivalent
	A
			MN		O
O := LIM(MN := A, IN := B, MX := C);			LIM
	B		IN
	C		MX
					O
O := LIM(MN := A, IN := B);	A		MN LIM
	B		IN

• The tables of

28.2 PRACTICE PROBLEMS

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1.