●
If a one-time timeout is tolerated, higher maximum runtimes can be al‐
lowed for the task. In this case, the ratio of average calculating time to
watchdog time is the one that is decisive. The maximum runtimes of
tasks mostly occur in one cycle or in a few cycles.
●
This time measurement is relatively inaccurate due to the resolution in
milliseconds for high demands with a tolerated maximum time of only
one or two milliseconds. This is why there is another way to measure
the available remaining time.
Example of a multitasking PLC ap‐
plication
Fig. 4-15:
Example of a multitasking PLC application
The above example shows the runtimes of three tasks with cycle times of
1 ms, 10 ms and 50 ms. The 1 ms task had a maximum runtime of 1 ms.
With a watchdog of, e.g., 2 ms, the reserve is ≥50%. The load of the 1ms
task is not obvious in this case.
The load of the 10ms task is a maximum of 2 ms. With a watchdog of, e.g.,
10 ms, the reserve is about 80%.
The load of the 50ms task is a maximum of 27 ms. With a watchdog of, e.g.,
50 ms, the reserve is about 45%.
Measuring idle time (P-0-1364)
The PLC function "MX_fGetFreeTicks" or parameter P-0-1364 can be used to
read the PLC idle time. The PLC idle time displays the unused calculating
time in the PLC time slot.
In a typical group of rapid and slow time-controlled tasks (without freewheel‐
ing task), the cyclic display of the idle time (e.g., with the oscilloscope) pro‐
vides a rough overview of the load of all tasks.
Extended runtime measurement
If necessary, the runtime of the PLC tasks can be measured more precisely.
This is particularly useful for rapid tasks (in a range of one to a few millisec‐
onds) which always have to be processed in their periodic time.
The time slot method is taken into account when measuring. The runtime of
the task is compared to its maximum possible runtime (according to the peri‐
odic time). The result is the load of each task in percent. When the calculat‐
ing time of a high priority task is increased, both its load and the load of the
Bosch Rexroth AG
DOK-INDRV*-MLD3-**VRS*-AP02-EN-P
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Rexroth IndraDrive Rexroth IndraMotion MLD (2G) as of MPx-18
Basic functions of Rexroth IndraMotion MLD
LSA Control S.L. www.lsa-control.com [email protected] (+34) 960 62 43 01