codesys "object reference not set to an instance of an object"

lesmar96

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May 2017
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SoMachine v.4.3 which is Schneider's version of Codesys.

I am writing a small program. One POU is in SFC But this message box pops up and says "object reference not set to an instance of an object" I get this message any time I try to build the program or log into the controller.

Everything works fine in all the POUs and it builds just fine until I add the program call for the SFC POU. Then I start getting this message. The SFC POU builds just fine without any errors, and it is only after I add the program call under task configuration that I start getting this message.

Any help on what is wrong?
 
I haven't used SoMachine but I do use TwinCAT (Beckhoff) which is also based on Codesys. I believe the "object reference not set to an instance of an object" error may have to do with instantiation of function blocks. You can't use a function block without creating a variable instance of it... in other words you can't just put a TON in your program, you have to create a variable myTON of type TON and call that. You likely know that already but it's something to double check.

I've found with TwinCAT that a program or FB isn't fully checked/verified during a build unless it's included in a call from the main POU. That may explain why the error doesn't show up until you add it to your task.
 
Not versed in TwinCAT but do you have a target specified. Going from memory but I have seen this message before and I seem to remember it coming up when there was no target hardware specified.
 
kolyur said:
I haven't used SoMachine but I do use TwinCAT (Beckhoff) which is also based on Codesys. I believe the "object reference not set to an instance of an object" error may have to do with instantiation of function blocks. You can't use a function block without creating a variable instance of it... in other words you can't just put a TON in your program, you have to create a variable myTON of type TON and call that. You likely know that already but it's something to double check.

I've found with TwinCAT that a program or FB isn't fully checked/verified during a build unless it's included in a call from the main POU. That may explain why the error doesn't show up until you add it to your task.
Click to expand...


I talked to Schneider tech support and they told me basically the same thing as this.

I was trying to find the issue and made some changes and the error has gone away, but I wasn't 100% sure which change I made caused the difference.
 

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