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Section 6 Program Code Issues Control Module Types

3BSE042835-600 91

Control Module Types

Code Sorting and Algebraic Loops

The code block sorting is a powerful tool that can be used to minimize delay

between input and output signals. This is achieved by dividing the code into

different code blocks in Control Builder. Code blocks can be used when information

is transmitted between objects in both directions using a structured data type. By

splitting the code into two or more code blocks it is possible to both send and

receive information within the same scan.

However, the situation is different when it comes to connections for example

reading and writing to single parameters. The basic principle is that an application

programmer should be allowed to write any IN parameter and read any OUT

parameter of a module without causing loops. This is achieved by writing to all

OUT parameters in a specific code block. This code block shall not contain anything

else but the writing to the OUT parameters. Local copies of the OUT parameters are

used in the other code blocks. These variables shall have the attribute nosort to avoid

loops. In order to secure that the output parameters are updated correctly, each of

these internal variables must be assigned in one code block only. If an output

parameter is dependant on calculations in more than one code block, there need to

be one internal variable with the intermediate result per code block.

For the parameter InteractionPar, the attribute “Nosort” is used under some

circumstances to prevent code loops. The code shall be written in such a way that no

component of InteractionPar is marked as "written".

A problem occurs when InteractionPar is passed into an internal Function Block as

an IN_OUT parameter. In this case, all components of InteractionPar shall have the

attribute "Nosort". This works fine in all cases except, when the order of assignment

of the components of InteractionPar is crucial. There is only one known case when

this order is crucial and that is when an "Apply" component is set. In this case, all

other components must be set before "Apply" is set.

Code tab names in control modules that begin with Start_ are sorted separately and

execute once before all other code in all other control modules in the application

after warm or cold start. The “Start_” feature can be used when a different code

sorting order is desired during initialization.

ABB AC 800M Library Object Style Guide

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