Programming manual M238 | 3 MB - BERGER - POSITEC

Function and Function Block Representation
Differences Between a Function and a Function Block
Function
Function Block
A function:
is a POU (Program Organization Unit) that returns one immediate result
is directly called with its name (not through an Instance)
has no persistent state from one call to the other
can be used as an operand in other expressions
Examples: boolean operators (AND), calculations, conversion (BYTE_TO_INT)
A function block:
is a POU (Program Organization Unit) that returns one or more outputs
is always called through an Instance (function block copy with dedicated name
and variables)
each Instance has a persistent state (outputs and internal variables) from one
call to the other
Examples: timers, counters
In the example below, Timer_ON is an instance of the Function Block TON:
228 EIO0000000384 04/2012