Applies To:
  • CitectSCADA 1.00, 1.01, 1.10, 1.11, 2.00, 2.01

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. 

The report should reset the bit in the PLC as the last thing it does. The code in the PLC should then wait a small time period before setting the bit again. This time will allow the report scheduler to read the off state of the bit and then the on state again. The time should allow for the maximum read cycle time of Citect for the particular PLC, typical 2..3 seconds.