3 Product Description HIMax System
HI 801 001 E Rev. 4.01 Page 40 of 122
Example 2: Safe Reaction within the Safety Time if an Interference is
Present
t
Cycle, Duration = Watchdog Time
Read-in Process in 1
st
Cycle
Read-in Process 2
st
Cycle
Read-in Process 3
rd
Cycle
Read-in Process 4
th
Cycle
Read-in Process 5
th
Cycle
Processing (in all Cycles)
Output Process in 1
st
and 2
nd
Cycle
Output Process in 3
rd
Cycle
Output Process in 4
th
Cycle
Output Process in 5
th
Cycle
Duration of Safety Time
Figure 10: Interference Triggers Safe Reaction
In example 2, valid input values are read within one cycle at
. For this cycle, the system
processes the valid input values, even though an interference occurred directly upon
completion of the read-in process.
If the interference is still present in the following cycle during the read-in process
, the
module detects the interference and the system decides if noise blanking can be performed
at this point in time based on the following rule:
Safety time - elapsed time - (2 * watchdog time) > 0
Noise blanking is possible in the 1
st
and 2
rd
cycle since the interference is present for less
than a cycle ( = elapsed time) and two additional cycles (2 * watchdog time) are available
for triggering a safe reaction. For this cycle, the system processes the last valid input
values of
and no defined fault reactions are triggered. The transient interference was
successfully blanked out.
As in example 2, two cycles are still available for the safe reaction in the ratio safety
time / watchdog time = 3/1.
If the interference is still present in the next read-in process
, the fault reaction must be
triggered in that cycle. The fault reaction must be triggered no later than when the outputs
are written to
since in the following output moment the safety time would be expired.
If noise blanking is not active, the system immediately triggers the defined fault reactions
during the read-in process
.
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