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5 Program processing, multitasking and system times
5.5 Direct peripheral access
5.4.0.4 Example: Watchdog deactivated
The interval time (IZ) is 10 ms.
Variant a: The interval time (IT) of a task was set to 10 ms.
The actual task time (TT) is 15 ms. The task is started on the first call but is
not terminated before the second cycle. Therefore, the task is not started
again in the second cycle. Only in the third cycle – after 20 ms – is it possible
to restart the task. The task does not run every 10 ms but rather only at a
time interval of 2 x 10 ms.
Variant b: The running cycle is not ended.
IZ = 10 ms
a TZ > IZ
IZ
TZ > IZ
b TZ > WZ
(endless loop)
IZ
IZ
TZ > IZ
IZ
IZ
IZ
TZ > IZ
TZ f WZ
Figure 41:Watchdog deactivated
5.4.1 Multiple tasks with the same priority
You can assign several tasks with the same priority. The tasks are split
according to the “Time Slice” principle and are practically executed
simultaneously as part intervals (Round Robin).
5.5 Direct peripheral access
The “Direct peripheral access” function enables access directly to the local
and central input and output signals of the control. The I/O access does not
occur via the input/output image. The local and central input and output
signals you can find the input and output signals of the CPU and the centrally
expanded XC-200 control with the XIOC signal modules. XIOC signal
modules which can be integrated via a bus system cant be accessed via the
“Direct peripheral access”.
Addressing is dependent on the slot number “0 to 15” of the signal modules.
Further differentiation within the slot exists and relates to bit number “0 to
max. 63” of the Inputs/Outputs.
Depending on the functionality of the XIOC signal modules, access occurs as
a bit/word or read/write operation. The access parameter indicates the
Table 8.
The inputs/outputs which are required for “Direct peripheral access” are
physically connected in the same manner as normal inputs/outputs.
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Modular PLC XC-CPU201-…(-XV), XC-CPU202-…-XV
06/14 MN05003001Z-EN
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