Block Types - Siemens SIMATIC S5 Manual

Introduction to STEP 5
OB 1
Level 1
2.3

Block Types

Table 2-2 lists the most important features of the block types:
Quantity
OB 1 to
OB 255
Max. length 8 Kbytes
Operations
set operations
(contents)
Representa- STL, CSF
tion methods LAD
Block header 5 words
length
Blocks calls JU, JC possible
only in FBs
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
Level 2
Figure 2-2. Nesting
Table 2-2. Comparison of Block Types
OB PB
255 256
1 2
PB 0 to
PB 255
8 Kbytes
Basic Basic
operations
, STL, CSF
6
LAD
6 6
5 words
JU, JC
. . . . . . .
. . . . . . .
Level 3 . . . . . . .
SB
256
2
SB 0 to SB 255 FB 0 to FB 255
8 Kbytes
Basic
operations
operations
, STL, CSF ,
6 6
LAD
6
5 words
JU, JC
S5-115F Manual
Level 16
FB DB
256 252
3
DB 4 to DB 255
4096
8 Kbytes
data words
Basic Bit pattern
supple-
mentary numbers
system texts
STL
5 words 5 words
JU, JC C, G
EWA 4NEB 811 6149-02
4
5