TwinCAT and Codesys - Function block FB_init array initialization
I have been using IEC 61131-3 function block FB_init methods quite a lot for different library blocks. They allow almost constructor-like initialization possibilities for function blocks. For example it’s quite useful to pass buffer size to a block using FB_init and then initialize a dynamic array using __NEW operator.
DataLogger : FB_Logger(BufferSize := 2000);
StateLogger : FB_Logger(BufferSize := 500);
METHOD FB_init : BOOL
VAR_INPUT
bInitRetains : BOOL; // if TRUE, the retain variables are initialized (warm start / cold start)
bInCopyCode : BOOL; // if TRUE, the instance afterwards gets moved into the copy code (online change)
BufferSize : UDINT;
END_VAR
//Code:
//Note this is not a fully working correct example
Buffer := __NEW(BYTE, BufferSize);
However I just had a situation that I needed to have array of function block instances that all have a FB_init parameter.
The Beckhoff Information System had an example of an array with different parameters, so I knew it was possible (phew).
PROGRAM MAIN
VAR
fbSample : FB_Sample(nInitParam := 1) := (nInput := 2, nMyProperty := 3);
aSample : ARRAY[1..2] OF FB_Sample[(nInitParam := 4), (nInitParam := 7)]
:= [(nInput := 5, nMyProperty := 6), (nInput := 8, nMyProperty := 9)];
END_VAR
However in my case the array size was based on a CONSTANT, the initial values were all the same and updating them manually would be too time-consuming. Finally I found that it’s possible, like the following (all instances get 123 to FB_init):
Example : ARRAY[0..ARRAY_MAXIMUM] OF FB_Block(123);
Here are the different possibilities for initialization.
//FB_Block
METHOD FB_init : BOOL
VAR_INPUT
bInitRetains : BOOL; // if TRUE, the retain variables are initialized (warm start / cold start)
bInCopyCode : BOOL; // if TRUE, the instance afterwards gets moved into the copy code (online change)
MyParam : INT;
END_VAR
//Code:
Prm := MyParam;
{attribute 'qualified_only'}
VAR_GLOBAL
//Single block instance
SingleFB_1 : FB_Block(MyParam := 1);
SingleFB_2 : FB_Block(1);
//Array of function block instances with different FB_init parameters
ArrayFB_1 : ARRAY[0..2] OF FB_Block[(MyParam := 1), (MyParam := 2), (MyParam := 3)];
ArrayFB_2 : ARRAY[0..2] OF FB_Block[(1), (2), (3)];
//Array of function block instances with same FB_init parameter
ArrayFB_3 : ARRAY[0..2] OF FB_Block(MyParam := 1);
ArrayFB_4 : ARRAY[0..2] OF FB_Block(1);
END_VAR
Results:
