Danfoss VLT 5000 Series Manual page 63

Response times
The existence of an interrupt is checked in a spe-
cial function which is also used as a watch dog
control. For this reason this is generally called up in
any procedure which could last somewhat longer
and in all loops, etc.
This procedure checks every 1 ms whether such
an event exists and, if necessary, sets a correspon-
ding flag. At the latest this flag is detected and
evaluated after the current APOS machine code
has been processed.
The response time is the maximum run time of the
machine code or 1 ms, whichever is greater. For
the VLT it is approx. 1 ms.
One exception is the time interrupt (ON TIME / ON
PERIOD). This checks whether the time has elap-
sed every 20 ms. Thus, it is not logical to define an
ON PERIOD with less than 20 ms.
NB!
Furthermore, in general, it is important to
make sure that interrupt functions do not
last too long. Particularly for ON PERIOD functions
it is important to ensure that the function does not
last longer than the period since otherwise a „jam"
of function procedure calls will be created.
Priorities
If two interrupt events should occur simultaneously
then the processing is prioritized as follows:
If two interrupt events should occur simultaneously
then the processing is prioritized as follows:
ON INT comes before ON COMBIT before
ON STATBIT before ON PARAM before ON TIME /
ON PERIOD but the other events are not lost.
Within the individual types of interrupts the
following is true:
ON INT / ON COMBIT / ON STATBIT
If two (input) interrupts occur simultaneously, then
the one with the lower number is executed first,
however the other is not lost. After the interrupt
procedure is completed the other is called up
accordingly.
If the same input resp. interrupt occurs again while
the procedure is being executed this is noted
again and subsequently executed.
Thus, an interrupt can only be lost if it occurs twice
during the execution of an interrupt procedure.
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ON TIME / ON PERIOD
As described above the execution time for every
temporal function is stored in an internal structure.
For simultaneous execution times the procedure
that is first on the list will be executed first. The
priority is thus determined by the sequence of the
ON PERIOD commands.
ON PARAM
If several of these interrupts occur simultaneously,
they are processed according to the sequence of
the ON PARAM commands in the program.
Interrupt nesting
It is not possible for one interrupt to be suspended
by another. Accordingly, while one interrupt is
being processed a second interrupt cannot be
processed. The only exception is the ON ERROR
function, which is also possible during the proces-
sing of interrupts.
However, an ON ERROR function cannot be sus-
pended by an interrupt.
NOWAIT in interrupts
In general, during an interrupt NOWAIT is set to
ON, that means that the program does not wait for
the completion of POSA commands.
This is necessary since otherwise a POSA com-
mand cannot be suspended by an interrupt proce-
dure, since this would immediately wait for the arri-
val of the axis. Thus, if you wish to wait for the
arrival of an axis during an interrupt procedure, this
must be done explicitly with WAITAX.
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