Siemens SIMADYN D Manual page 74

Cycle errors
NOTE
T1+T2
T1
T2
T3
Interrupt
task
T1
Fig. 2-12 Sequence of a configured task
System- and communication configuring D7-SYS - SIMADYN D
Edition 03.2001
If a task can no longer be completed within a basic sampling time due to
a higher computation time, then it is completed in the following basic
cycles. The tasks with short sampling times are completed before tasks
with long sampling times, i. e. T1 before T2, before T3 before T4 before
.... This distribution is permissible, i. e. without cycle error, as long as the
required sampling times are maintained (refer to the 2nd and 3rd cycle).
If the computation time loading becomes higher, for the task with the
longest sampling time, at same stage a cycle error will occur. This means
that the sum of the function blocks cannot be computed completely within
the configured sampling time.
If a specific number of cycle errors is exceeded, an "E" error ID is set,
and is displayed in the 7-segment display on the front panel of the CPU,
if this is the highest priority error status of the CPU at this time.
In addition to the configurable interrupt tasks, the cyclic tasks are
interrupted, especially by communication interrupts. These interrupts
ensure that, for example, the data to be transmitted and received via the
serial interfaces is processed before new data is received. Transmit- and
receive interrupts such as these can occur independently of the
configured cycle time of the appropriate communication blocks at almost
any instant in time. As result of this, and the unpredictable occurrence of
interrupt tasks, if the process utilization is extremely high, each cyclic task
can generate one or several cycle errors due to task back-up.
This can be especially noticed, if
• the utilization by the task with the lowest sampling time is extremely
high, and
• the functions computed in this task are extremely sensitive to sporadic
sampling cycle failures, (e. g. closed-loop position controls).
T1+T3
T2
T1+interrupt task+T4
T1+T2
T3
Systemsoftware
T1
In this
T2 = 2 * T1
T4
T3 = 4 * T1
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