Technical data

Table Of Contents
Organization Blocks
System Software for S7-300/400 System and Standard Functions - Volume 1/2
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A5E00709327-01
1.5 Cyclic Interrupt Organization Blocks (OB30 to OB38)
Description
S7 provides up to nine cyclic interrupt OBs (OB30 to OB38) which interrupt your
program at fixed intervals. The following table shows the default intervals and
priority classes for the cyclic interrupt OBs.
OB Number Default Interval Default Priority Class
OB30 5 s 7
OB31 2 s 8
OB32 1 s 9
OB33 500 ms 10
OB34 200 ms 11
OB35 100 ms 12
OB36 50 ms 13
OB37 20 ms 14
OB38 10 ms 15
Understanding the Operation of Cyclic Interrupt OBs
The equidistant start times of the cyclic interrupt OBs are determined by the
interval and the phase offset. Refer to /234/ for the relationship between the start
time, time cycle, and phase offset of an OB.
Note
You must make sure that the run time of each cyclic interrupt OB is significantly
shorter than its interval. If a cyclic interrupt OB has not been completely executed
before it is due for execution again because the interval has expired, the time error
OB (OB80) is started. The cyclic interrupt that caused the error is executed later.
You can disable or delay and re-enable cyclic interrupts using SFCs 39 to 42
Refer to the specifications of your specific CPU for the range of the parameters
interval, priority class, and phase offset. You can change the parameter settings
using STEP 7.