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Chapter 9 PLC Operation
9-7
(3) Continuation of operation after a congestion error occurred
If an interrupt scan congestion error occurs when the special internal output bit R7C2, which specifies whether the
operation should continue after a congestion error, is turned on, the interrupt scan is started anew and the scan is
executed from the beginning again. Therefore, if the operation continuation specification of the normal scan is Off under
the conditions where interrupt inputs are frequently entered from the external source, this scan is stopped as a normal
scan congestion error. If the operation continuation specification of the normal scan is On, only interrupt scans are
continuously executed depending on the condition of the interrupt congestion error. Care must be taken because normal
scans are not executed under this condition.
Figure 9.14 Operation when operation continuation at congestion error is set
INT16
INT16
INT16
Normal
scan
END scan processing
Program execution
Periodical system processing
Interrupt analysis
processing
Interrupt scan
Congestion check time
Interrupt contact on
Interrupt
scan
Interrupt contact on
Interrupt contact on
R7C0 On/R7C2 On: Continue
R7C0 Off/R7C2 On: Stop