Unresolved extenal variables

AC800M

I have a Function Block that uses external variables.

I have set up MMS access variables that are using the same name syntax as the Function Block,

but get "Unresolved external variable ExternalBool1..." when attempting to download the program.

Thanks in advance

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RDPLC Rank: 855

Asked 3 years ago

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> "Would it be better practice to use parameters rather than external variables ?"

Yes. There are a number of issues using External parameters - mostly around "good programming practice". External parameters are more of a problem when you're distributing libraries because of the requirement to have fixed global variable names. They can also be very difficult to document, trace and troubleshoot in large applications.

External variables are usefull to solve some particular problems, but overall should be considered a "bad idea".

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