Technical data

2.3 Function Blocks
Function blocks (FB/FX) are also parts of the user program just like
program blocks. FX function blocks have the same structure as FB
function blocks and are programmed in the same way.
You use function blocks to implement frequently recurring or very
complex functions. In the user program, each function block represents a
complex complete function. You can obtain function blocks as follows:
•• as a software product from SIEMENS (standard function blocks
on diskette - see /11/ in Chapter 13); with these function blocks
you can generate user programs for fast and simple open loop
control, signalling, closed loop control and logging;
or
•• you can program function blocks yourself.
Compared with organization, program and sequence blocks, function
blocks have the following four essential
differences:
OB, PB, SB FB/FX
1. Range of operations
only basic operations - basic operations,
- supplementary operations
- system operations
2.
Method of representation
programming and call
in STL, LAD, CSF
programming only in AWL
3.
Name
name environment not
possible
(only number)
in addition to the number
a name with max. 8 chars. can
be assigned
4.
Operands
none formal operands (block
parameters).
When the block is called
formal operands are assigned
actual operands
2
Function Blocks
CPU 928B Programming Guide
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