Beginner having troubles with TwinCAT 3 basics

Lamaman · May 5, 2021

Hello!
I'm a complete beginner to programming and i have a project i'm working on in TwinCAT 3 since i'm using a Beckhoff PLC.

One of the problems i have, is this:

Variable1 :=TRUE; //test
IF Variable1= TRUE
THEN Variable2 := TRUE;
Variable3:= TRUE;
ELSE Variable2:= FALSE;
Variable3:= FALSE;
END_IF

I have defined all the variables. If i start the program , then only variable2 reacts to change in variable1. Variable3 stays false.
I have tried adding an AND before Variable3, but that makes no change.

I'm new to this forum and i hope what i'm explaining makes sense.
I have managed to solve some problems myself but can't wrap my head around this one. Seems to be a simple logic task but it wont work.

Anyway, can anyone tell where seems to be the problem?

kalabdel · May 5, 2021

Lamaman said:
Hello!
I'm a complete beginner to programming and i have a project i'm working on in TwinCAT 3 since i'm using a Beckhoff PLC.

One of the problems i have, is this:

I have defined all the variables. If i start the program , then only variable2 reacts to change in variable1. Variable3 stays false.
I have tried adding an AND before Variable3, but that makes no change.

I'm new to this forum and i hope what i'm explaining makes sense.
I have managed to solve some problems myself but can't wrap my head around this one. Seems to be a simple logic task but it wont work.

Anyway, can anyone tell where seems to be the problem?

The statements are executed in order, first if to elsif.........else. A true condition causes the program to executed the code for this specific condition then *breaks" out and continues at the end_if.

Edit: use a breakpoint and step into the code to see order of execution, while changing the value of different tags.

kalabdel · May 5, 2021

What happened the topic started a few weeks ago for YouTube TwinCat tutorials. Can't seem to find it and it was quite good. Look for alltwincat on Google and YouTube.

kolyur · May 5, 2021

Your original code should work. If Variable3 isn't turning on, make sure it isn't being overwritten somewhere else. Just to clean it up a bit:

Code:

Variable1 := TRUE; //test

IF Variable1 THEN
   Variable2 := TRUE;
   Variable3 := TRUE;
ELSE
   Variable2 := FALSE;
   Variable3 := FALSE;
END_IF

It isn't necessary to say 'IF Variable1=TRUE'... since it's a boolean variable it will evaluate to true or false without the equal sign.

You could get the same functionality with this:

Code:

IF Variable1 THEN
   Variable2 := Variable3 := TRUE;
ELSE
   Variable2 := Variable3 := FALSE;
END_IF

or this:

Code:

Variable2 := Variable3 := Variable1;

kalabdel · May 5, 2021

I still can't find the topic! But here's link to his youtube
This guy is also very good and is now doing some motion control tutorials. He has basic stuff in his channel, just browser for it.

Beginner having troubles with TwinCAT 3 basics

Lamaman

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kalabdel

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kalabdel

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kolyur

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kalabdel

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