ISPSoft User Manual

Chapter 7 Function Block
7.1.2 Characteristics and Advantages of Function Blocks
Owing to the fact that function blocks present characteristics and advantages that traditional
programming of a PLC does not have, function blocks are supported by IEC 61131-3, and are
widely used by users.
• Modular design
A large program is divided into several subroutines, and the subroutines are created as function
blocks. The function blocks are arranged and called by POUs of the program type.
• Highly independent
Different function blocks can be created by means of different programming languages such as a
ladder diagram, an instruction list, a structured text, and a function block diagram according to the
characteristics of the function blocks or a programmer’s habit. Besides, when a POU calls a
function block, the programming language by which the program in the function block is written
does not need to be considered. For example, if a complex operation has to be performed in a
part of a ladder diagram, users can create the part of the ladder diagram as a function block by
means of a structured text, and the function block can be called by the original ladder diagram.
• Reusable
Once a function block is created, it can be used repeatedly as long as users conform to the rule of
using the function block.
• Highly portable
After a function block is created, it can be used in the original project. Besides, after the function
block is exported, it can be imported into another project. As a result, users can gradually create
their own function blocks.
• Function blocks can be maintained conveniently.
The program in a function block is an independent module. If an error occurs in a function block,
or the function of a function block does not meet the actual requirement, users can just modify the
program in the function block, and do not need to debug or modify the whole program,
• The readability of a program is increased.
Users can write a complex program or a program which will be used repeatedly in a function
block, and the function block can be called by the original program. The structure of the original
program becomes more simplified, and the program becomes more readable.
• Highly confidential
After users set a password for a function block created, they can create their own core technology
in the function block without care, and provide the function block for other users. Besides, system
suppliers or software developers can provide function blocks which have specific functions for
customers.
• Highly efficient
The application of function blocks provides a highly efficient development environment in terms of
project development. Owing to the fact that function block are modular, developers and
manufacturers can take part in the development of a project together, and the use of human
resources are more flexible.
7.2 Structure of the Function Blocks in ISPSoft
Please refer to the following figure. The internal structure of a function block is similar to that of a
POU of the program type. It is composed of a local symbol table and a program. A function block is
edited in a way in which a POU of the program type is edited. The programming languages that
users can make use of to create the function blocks in ISPSoft are ladder diagrams, instruction lists,
structured texts, and function block diagrams, but are not sequential function charts. Besides, a
function block can call another function block. When a function block is called, the programming
language by which program in the function block is written does not need to be considered.
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