ABB AC 800M, Руководство по стилю объекта библиотеки

Страница: 93 / 120

Section 6 Program Code Issues Function Block Types
3BSE042835-600 93
Function Block Types
Even though there are no code sorting of code blocks within a function block type,
the code might be split into more than one code block. This make the code more
readable, especially for objects that implements different, non dependant functions.
In SIL application there is an increase of execution time for each switch between
code blocks, so the number of code blocks should be minimized.
Diagram Types
Diagrams are created under an application, and diagram types (which can be reused
as instances in a diagram) are created under a library or under the same application
as the diagram.
The FD code blocks in diagrams and diagram types allow mixing of functions,
function blocks, control modules, and other diagrams, and graphically connect them
to achieve a particular logic. The code in the function blocks is sorted according to
the placement in the diagram, and the code in the control modules are sorted
according to the data flow order. The actual execution order is indicated on each
instance in the diagram. The code sorting of the diagram has to be considered when
designing a diagram type. The use of function block types and control module types
with a diagram type has to be done with a understanding of how the code are sorted
in the diagram type. Signals in backward direction (components with reverse
attribute) cannot be handled by Split or Join elements. Instead, these signals must be
handled in a separate Structured Text code block in the same manner as in control
modules.
Data Types
Data types common to several libraries shall be placed in a supporting library.
Changing of initial values can be realized through project constants.
The data types can be divided into three categories:
1. Private data types, not used in parameters or in sub-data types in parameters.
Should have attributes Private and Hidden and have a complete description of
all components as well as the type itself.
2. Internal data types, where the content is of no importance for the user for
example graphical connections where the user has no interest of the single