| If you schedule a report on a bit in the
PLC and the report resets that bit, it is possible for the report
to lock up waiting for the bit forever. The report scheduler will
run a report that is triggered on a bit when it sees the bit go
from 0 to 1, ie on the rising edge of the transition. If the bit is
reset to 0 and then quickly back to 1 again, the report scheduler
may not see the bit at 0. The report scheduler will see the bit as
having been on continuously and will not run the report..
Normally this type of report will reset the bit that trigged it,
or another bit to signal back to the PLC that it has completed.
When the PLC sees the report has reset the bit, it may set the bit
again to request another report. If this happens quickly then the
report scheduler will not see the bit go off and will not schedule
the report. In this state the report scheduler is waiting for the
PLC and the PLC is waiting for the report scheduler and the report
will never run again. |
