Introduction to STEP 5 S5-115F Manual
Figure 2-2. Nesting
Level 1 Level 2 Level 3 Level 16
OB 1
. . . . . . .
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2.3 Block Types
Table 2-2 lists the most important features of the block types:
Table 2-2. Comparison of Block Types
PB SB FB DBOB
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Quantity
255
1
OB 1 to
OB 255
256
2
PB 0 to
PB 255
256
2
SB 0 to SB 255
256
3
FB 0 to FB 255
252
4
DB 4 to DB 255
8 Kbytes 8 Kbytes 8 Kbytes 8 Kbytes
4096
data words
5
Max. length
Basic
operations
Operations
set
(contents)
Basic
operations
Basic
operations
Bit pattern
numbers
texts
Representa-
tion methods
STL, CSF
6
,
LAD
6
STL, CSF
6
,
LAD
6
STL, CSF
6
,
LAD
6
5 words 5 words 5 words 5 words 5 words
JU, JC possible
only in FBs
JU, JC JU, JC JU, JC C, G
Block header
length
Blocks calls
STL
Basic
supple-
mentary
system
operations
1 The operating system can call special OBs by itself ( 2.3.1 and 6.2).
2 When using standard function blocks, do not use parameter ”0”.
3 Special function blocks are already integrated in the operating system ( 6.1).
4 Data blocks DB 0 and DB 1 are reserved for the block address list, the configuration DB and the error DBs.
5 A data block can be referenced up to DW 255 with ”L DW” or ”T DW”, with DB 2 and DB 3 reserved as error DBs.
6 The possible basic operation set is limited for the CSF and LAD methods of representation ( Table 2-1).
2-6
EWA 4NEB 811 6149-02
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