I have declared 22 signal in real M blocks ,while my downloading time ,22 loop error is coming

I have declared 22 signal in real M blocks in sil2 ,while download time I am facing 22 loop error regarding compiler switch .because compiler switch settings for control module loop not enabled ,suppose I enabled means there is no error ,can I change compiler setting and download pls help.

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jaikumar 007 Rank: 390

Asked 2 years ago

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You should fix the code loops !

Code loops occur when you read from and write to the same variable in the same program scan and the compiler cannot decide which should happen first. The compiler resolves this problem by simply executing your control modules in a "random" order.

This can lead to unpredictable results in some cases.

Only ever ignore code loops if you are sure you know why they have occured and that they will not affect the operation of your program. The most common reason for code loops is a programming error.

There is a setting in the options menu that allow you to download code even when loop errors are present. You cannot disable the warnings.

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by Tung Dao Rank: 173 on 1/14/2017 10:40:59 AM | Like (0) | Report

Hi Rob.

I don't think the compiler execute the code in a random order. There are some rules for which code to be executed first such as within one SCM, code tab from left to right.
Do you think so?

by Rob Lyon AKS expert

Rank: 2 on 1/14/2017 11:50:26 AM | Like (0) | Report

No.

These rules only apply when you use "standard" IEC-61131 programming languages. ie program POU's.

Whenever you use Control Modules, the compiler automatically sorts the execution order - not of the control modules - but the code blocks inside the control modules. With control modules, code blocks absolutely do NOT execute from left to right. They execute in the "optimized" order. When a code loop occurs, there is no optimized order and the execution order truly is arbitrary. This can cause some really annoying and impossible to find timing errors when the execution order changes because you added some code somewhere else and variables like flags are only set for one program scan or have other timing dependencies.

We could argue long and hard about code sorting. Personally I'm not a fan, but it does have uses in some particular types of application. It's important to remove code sorting errors as soon as they appear because they can be extremely difficult to remove later in the project.

by Tung Dao Rank: 173 on 1/14/2017 11:26:03 PM | Like (0) | Report

Hi Rob.

I believe code blocks are executed from left to right for Control Modules also. I create a simple Control Module to test, left code has A:= B, right code has A:= not B and I never see A = B.

I think the compiler was just trying to warn us that the first command will be disregarded by the second command while we have totally control on which command should be first.

by Rob Lyon AKS expert

Rank: 2 on 1/15/2017 12:44:25 AM | Like (0) | Report

3BSE044222-511 - AC800M Planning, Section 3, Code Sorting explains the concept and gives suggestions on how to resolve code loops.

by Tung Dao Rank: 173 on 1/15/2017 12:52:55 AM | Like (0) | Report

Thanks Rob.

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Rob Lyon

Rank: 2

Answered 2 years ago

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I have declared 22 signal in real M blocks ,while my downloading time ,22 loop error is coming

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