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2.3
Function Blocks
CPU 948 Programming Guide
C79000-G8576-C848-04
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/); 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
1.
only basic operations
2.
programming and call
in STL, LAD, CSF
3.
name environment not
possible
(only number)
4.
none
Range of operations
- basic operations,
- supplementary operations
- system operations
Method of representation
programming only in AWL
Name
in addition to the number
a name with max. 8 chars. can
be assigned
Operands
formal operands (block
parameters).
When the block is called
formal operands are assigned
actual operands
Function Blocks
FB/FX
2 - 23
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