Siemens SIMATIC S5 Manual page 86

Introduction to STEP 5
• Initialization of time intervals for processing OB 13
The time interval is transferred to the S5-115F operating system via COM 115F.
• Saving data
If a time interrupt service OB uses scratch flags that are also used in the cyclic control program,
these flags must be saved in a data block during processing of the OB.
OB 21/22: Setting the restart characteristics
OB 21 is processed on a manual restart (programmer selection, mode selector), OB 22 on a cold
restart after power failure ( Figure 2.5). You program these blocks to obtain specific presettings.
If OB 21 or OB 22 is not programmed, the system branches directly into the "RUN" mode (cyclic
program scanning).
Features of the restart blocks (OB 21, OB 22) include the following:
• Timers are processed
• Scan time monitoring is not activated
• Interrupt blocks are not processed
• Digital output modules are disabled
Mode selector STOP RUN
programmer RUN command
Clearing of process image, timers,
counters and flags
Call OB 21
OB 251 PID algorithm ( 6.2)
2-12
Enable outputs
Read in PII
Call OB 1
Output PIQ
Figure 2-5. Setting the Restart Characteristics
Restart after POWER UP
Clearing of process image, timers,
counters and flags
Call OB 22
S5-115F Manual
EWA 4NEB 811 6149-02