Calling a Function Block
CAL, CALC, CALNC, CALCN

A function block ( ) groups an algorithm and a set of private data. It has inputs and outputs. A function block can be:

• a standard function block (RS, TON...)
  
• a User-Defined Function BlockA function block groups an algorithm and a set of private data. It has inputs and outputs. (UDFB"User Defined Function Block" UDFB can be used as a sub-function block in another program of the application. It is described using FBD, LD, ST or IL language. Input / output parameters of a UDFB (as well as private variables) are declared in the variable editor as local variables of the UDFB) written in ST"Structured text" A high-level language that is block structured and syntactically resembles Pascal, FBD"Function block diagram" A function block diagram describes a function between input variables and output variables. A function is described as a set of elementary blocks, FFLD or IL"Instruction list" This is a low-level language and resembles assembly

To use a function block, you have to declare an instance of the block as a variable, identified by a unique name. Each instance of a function block as its own set of private data and can be called separately. A call to a function block instance processes the block algorithm on the private data of the instance, using the specified input parameters.

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• Best Practice: It is recommended that function blocks be put in an N step and not in P0 or P1, as those steps are executed only once. If you must use an FB in P0 or P1 be sure to call it again in the N state so it may finish.

ST Language

To call a function block in ST, you have to specify the name of the instance, followed by the input parameters written between parentheses and separated by comas. To have access to an output parameter, use the name of the instance followed by a dot '.' and the name of the wished parameter. The following example demonstrates a call to an instance of TON function block:

(* MyTimer is declared as an instance of TON *)
MyTimer (bTrig, t#2s); (* calls the function block *)
TimerOutput := MyTimer.Q;
ElapsedTime := MyTimer.ET;

FBD and FFLD Languages

To call a function block in FBD or FFLD languages, you just need to insert the block in the diagram and to connect its inputs and outputs. The name of the instance must be specified upon the rectangle of the block.

IL Language

To call a function block in IL language, you must use the CAL instruction, and use a declared instance of the function block. The instance name is the operand of the CAL instruction, followed by the input parameters written between parentheses and separated by comas. Alternatively the CALC, CALCN or CALNC conditional instructions can be used:

CAL	calls the function block
CALC	calls the function block if the current result is TRUE
CALNC	calls the function block if the current result is FALSE
CALCN	same as CALNC

The following example demonstrates a call to an instance of TON function block:

(* MyTimer is declared as an instance of TON *)
Op1: CAL   MyTimer (bTrig, t#2s)
FFLD       MyTimer.Q
ST         TimerOutput
FFLD       MyTimer.ET
ST         ElapsedTimer

Op2: FFLD  bCond
CALC  MyTimer (bTrig, t#2s)  (* called only if bCond is TRUE *)
Op3: FFLD  bCond
CALNC  MyTimer (bTrig, t#2s)  (* called only if bCond is FALSE *)

See also:

Differences Between Functions and Function Blocks