Organization Blocks (Obs); Blocks - Siemens SIMATIC S5 Manual

S5-115F Manual
Block structure
Each block consists of the following:
• Block header specifying the block type, number, and length.
The programmer generates the block header when it transforms the block.
• Block body with the STEP 5 program or data.
Absolute
byte addresses
(in ascending
order)
Programming
Program your blocks as follows (does not apply to data blocks):
1. Specify the block type (e.g. PB).
2. Specify the block number (e.g. 27).
3. Enter the control program statements.
4. Terminate the block with the "BE" statement.
2.3.1

Organization Blocks (OBs)

Organization blocks form the interface between the operating system and the control program.
Organization blocks are handled in either of the following two ways:
• The operating system calls them cyclically, in response to events or at certain times.
• The control program can call them as operating functions ( 6.2).
Table 2-3 provides an overview of organization blocks.
All organization blocks can be programmed with parameters from the permissible range of 0 to
255. However, they must be called in the control program.
All OBs must start with the LPLZ (logical program counter) sequence of operations ( 3.8):
• LFW0
• LKF+1
• +F
• TFW0
EWA 4NEB 811 6149-02
Figure 2-3. Structure of a Block Header
Introduction to STEP 5
Synchronization
pattern
Block type
Block number
Programmer ID
Library
number
Block length
2-7