Siemens SIMATIC S7-200 System Manual page 56

S7-200 Programmable Controller System Manual
The S7-200 Allows Your Program to Interrupt the Scan Cycle
If you use interrupts, the routines associated with each interrupt event are stored as part of the
program. The interrupt routines are not executed as part of the normal scan cycle, but are
executed when the interrupt event occurs (which could be at any point in the scan cycle).
Interrupts are serviced by the S7-200 on a first-come-first-served basis within their respective
priority assignments. See the Interrupt instructions in Chapter 6 for more information.
The S7-200 Allows You to Allocate Processing Time for Run Mode Edit
and Execution Status
You can configure a percentage of the scan cycle to be dedicated for processing a run mode edit
compilation or execution status. (Run mode edit and execution status are options provided by
STEP 7--Micro/WIN to make debugging your program easier.) As you increase the percentage of
time that is dedicated to these two tasks, you increase the scan time, which makes your control
process run more slowly.
The default percentage of the scan dedicated to processing run mode edits and execution status
is set to 10%. This setting was chosen to provide a reasonable compromise for processing the
compilation and status operations while minimizing the impact to your control process. You can
adjust this value by 5% increments up to a maximum of 50%. To set the scan cycle time-slice for
background communications:
1. Select the View > Component >
System Block menu command
and select Background Time.
2. In the Background tab, use the
drop down box to select the
communications background time.
3. Click OK to save your selection.
4. Download the modified system
block to the S7-200.
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Figure 4-19 Communications Background Time