In codesys some functions support what in other languages is usually called 'params', i.e. a function that can take a varied amount of similarly typed variables. For example the ADD Operator (function in ladder).
My question is, if there's any way to do the same in user defined functions?
The only idea that I have so far is to take an ARRAY [*] OF SOMETHING and use LOWER_BOUND and UPPER_BOUND to do the computations. This does work, but requires the user to create an additional array variable every time they want to call my function. For example, we have the CONCAT function that concatenates 2 strings. Suppose I want a CONCAT_ALL function that takes n strings and concatenates them all:
STRS: ARRAY [0..9] OF STRING := [STR1, STR2, STR3, STR4, STR5, STR6, STR7, STR8, STR9, STR10];
// This works, but I want to avoid creating an array variable!
CONALL1: STRING := CONCAT_ALL(STRINGS := STRS);
// This doesn't work!
CONALL2: STRING := CONCAT_ALL(STRINGS := [STR1, STR2, STR3, STR4, STR5, STR6, STR7, STR8, STR9, STR10]);
(EDIT: As I was asked, I am using Schneider Electric Machine Expert 1.2, or CODESYS compiler 3.5.12.80)
There is hope in the future!
In Codesys V3.5 SP16 it seems to be finally possible to use FUNCTIONs and METHODs with optional arguments. Of course this will be in non-codesys products, like TwinCAT and Schneider, in later versions.
This means you can finally create a CONCAT with 100 arguments and call it with just for example 3! Awesome.
https://www.codesys.com/fileadmin/data/Images/Download/features-and-improvements-V35SP16-en.pdf
Here is an object oriented example of a string concatenator Function Block:
First we define an Interface with 2 methods:
INTERFACE I_MultipleConcat
METHOD concatString : I_MultipleConcat
VAR_INPUT
sTarget : STRING;
END_VAR
METHOD getResult
VAR_IN_OUT
sRetrieveResult : STRING(1000);
END_VAR
Then the Function Block which implements the Interface:
FUNCTION_BLOCK FB_MultipleConcat IMPLEMENTS I_MultipleConcat
VAR_OUTPUT
uiLen : UINT;
END_VAR
VAR
sResult : STRING(1000);
END_VAR
//-------------------------------------------------------------------
METHOD concatString : I_MultipleConcat
VAR_INPUT
sTarget : STRING;
END_VAR
//make sure that the length of sResult is not exceeded
IF uiLen + INT_TO_UINT(LEN(sTarget)) <= (SIZEOF(sResult)-1)
THEN
//add uiLen as offset to sResult memory access
memcpy(ADR(sResult) + uiLen,ADR(sTarget),LEN(sTarget));
uiLen := uiLen + INT_TO_UINT(LEN(sTarget));
END_IF
//return the instance of this FuncBlock in order to concat new strings
//with concatString() or pass the result to another STRING with getResult()
concatString := THIS^;
//-------------------------------------------------------------------
METHOD getResult
VAR_IN_OUT
sRetrieveResult : STRING(1000);
END_VAR
sRetrieveResult := sResult;
sResult := '';
uiLen := 0;
You can call it like this:
IF NOT bInit
THEN
bInit := TRUE;
//s1 must be a STRING(1000) otherwise compile error
fbMultipleConcat
.concatString('Test1 ')
.concatString('Test2 ')
.concatString('Test3 ')
.getResult(s1);
END_IF
Short answer: There is no way to pass n arguments to a function.
Structured text is a strongly and statically typed language designed for hard real time requirements and it is not a scripting language like Python.
If you have a lot of string manipulations in your code that you don't want to do in python but in your real time loop (and you should assess if it's really necessary depending on your requirements) and still want to make it in a comfortable way, then you have to put some effort in it and build a string manipulation library yourself.
After that you could have a very comfortable function call like this:
sResult := F_Concat6(str1,str2,str3,str4,str5,str6);
I understand that it is tempting to adopt thought and programming patterns learned from other programming languages, but structured text and real time industrial control programming is really another kind of beast compared to common user land programming.
With that I mean, that there are specific reasons why the language is designed as it is and when those principles are correctly understood and applied, rock solid architectures derive from them.
To sum it up, my two cents of advice on this:
Think and write software as expected by your domain and do not port incompatible working methods from other domains.
No you cannot pass n arguments to function.
But you can pass an array, with none fixed number of elements. Syntaxyx for Codesys 2.3.
FUNCTION CONCAT_ALL : STRING(250)
VAR_INPUT
asParts: POINTER TO ARRAY[0..10000] OF STRING(20); (* Array of strings *)
iNum: INT; (* Number of elements *)
END_VAR
VAR
iCount: INT; (* For cycle *)
END_VAR
FOR iCount := 0 TO 10000 DO
IF iCount > iNum THEN
EXIT;
END_IF;
CONCAT_ALL := CONCAT(CONCAT_ALL, asParts^[iCount]);
END_FOR;
END_FUNCTION
PROGRAM PLC_PRG
VAR
(* Array 1 to test *)
asTest1: ARRAY[1..2] OF STRING(20) := 'String 1', 'String 2';
(* Array 2 to test *)
asTest2: ARRAY[1..3] OF STRING(20) := 'String 1', 'String 2', 'String 3';
s1: STRING(250);
s2: STRING(250);
END_VAR
s1 := CONCAT_ALL(ADR(asTest1), 2);
s1 := CONCAT_ALL(ADR(asTest2), 3);
END_PROGRAM
Is it possible to store a variable value in each PLC cycle? I need the first 10 values each time to perform some calculations. I am using the OpenPCS platform and ST for programming.
You can create an array of values and then store as array values
VAR
aBuffer : ARRAY[1..32] OF WORD;
init:BOOL; (* Init array *)
rest:BOOL; (* Reset *)
val:WORD; (* Value *)
iCount:INT; (* Array index *)
END_VAR
VAR_TEMP
iTmp : INT;
END_VAR
iTmp := UINT_TO_INT(N) - 1;
IF NOT init OR rest THEN
init := TRUE;
FOR iCount := 1 TO iTmp DO
aBuffer[iCount] := val;
END_FOR;
END_IF
iCount := INC1(iCount, 32);
aBuffer[iCount] := val;
This is a code example that created 32 elements array and every new PLC cycle assign new element and rotates.
After that, you can calculate the average or min and max.
INC1 increments given value by one until it reaches 32 and then reset to 1.
I need to run some code every time the PLC starts. This code should only be run once and then never again until the PLC is restarted. I initialize some global variables and validate the persistent data before allowing the main PLC to run. This is because the actions of the machine can be damaging if some of these variables are not setup correctly.
Is there a way to start/stop the other PLC tasks? I noticed TwinCAT doesn't support initialization and shutdown interrupts for PLC tasks.
TwinCAT has a 'PlcTaskSystemInfo' struct containing a boolean for FirstCycle. You can use that to run the initializing code only once.
VAR fbGetCurTaskIdx: GETCURTASKINDEX; (* Further example+explanation in Infosys *)
fbGetCurTaskIdx();
IF _TaskInfo[fbGetCurTaskIdx.index].FirstCycle THEN
(* Initialization code here *)
ELSE
(* Normal code here *)
END_IF;
I don't know of a way to start/stop individual PLC tasks. You can start/stop a runtime though.
But perhaps it can be as simple as this code below, which will only run when your PLC starts.
VAR initialized: BOOL := FALSE;
IF NOT initialized THEN
(* Run your initialization code here *)
initialized := TRUE;
END_IF
(* Rest of your program here *)
Edit:
I used a state machine inside the initialization code to help with the task allowed time issue.
Example:
VAR
Initialized : BOOL := FALSE;
Init_State : UINT := 0;
END_VAR
IF NOT Initialized THEN
(* Initialization State Machine *)
CASE Init_State OF
0: (* First step in initialization *)
Init_State := Init_State + 1;
1: (* Second step in initialization *)
Init_State := Init_State + 1;
.
.
.
n: (* Last step in initialization *)
Initialized := TRUE;
END_CASE
END_IF
I have a input variable c_timTransmissionRate which is usually initalized using the persistent variable list. The default value for the persistent variable list in the function block TxRaw is then overriden by the instanciating function block ´TxDbc´. This again is application specific overriden in the persistent variable list itself.
In a few cases the value for c_timTransmissionRate is provided dynamically by the instanciating function block TxTsc1 during runtime.
My problem is that I currently always see the original TIME#0ms value in the debugger instead of the values given in the persistent variable list.
Extract of my current code:
FUNCTION_BLOCK TxRaw
VAR_INPUT PERSISTENT CONSTANT
c_timTransmissionRate : TIME := T#0ms;
END_VAR
(* instructions *)
END_FUNCTION_BLOCK
FUNCTION_BLOCK Tx
VAR
tx : TxRaw;
END_VAR
(* instructions *)
tx();
(* instructions *)
END_FUNCTION_BLOCK
FUNCTION_BLOCK TxTsc1 EXTENDS Tx
(* instructions *)
tx.c_timTransmissionRate := PI()*THUMB();
SUPER^();
END_FUNCTION_BLOCK
FUNCTION BLOCK TxDbc EXTENDS Tx
VAR
tx : TX := (c_timTransmissionRate := T#20ms);
END_VAR
(* instructions *)
SUPER^();
END_FUNCTION_BLOCK
This is a solution for mutual exclusion problem from one of my exercises:
var blocked : array[0..1] of boolean; (* blocked is an array of two Boolean elements *)
turn : 0..1; (* turn can have value 0 or 1 *)
procedure P ( id : integer )
begin
repeat
blocked[id] := true;
while turn ≠ id do
begin
while blocked[1 – id] do; (* a do-nothing loop to implement busy waiting *)
turn := id
end;
< critical section >
blocked[id] := false;
< remainder of procedure >
until false
end;
begin (* main program *)
blocked[0] := false; blocked[1] := false;
turn := 0;
parbegin (* begin parallel execution of processes *)
P(0); P(1) (* invoke two concurrent processes, both to execute procedure P *)
Parend (* end parallel execution *)
end.
I am unable to understand when exactly a process executes particular statement in the code above. I know we can have multiple execution scenarios.
I want to know if this uncertainty of order of execution exists all the time.
And, is there any way to figure out what execution scenario will occur?
Thanks!