Chapter 5 Program Configuration and Operation Method
5.1.3 Scan time
The processing time from program step 0 to the next step 0 is called ‘Scan Time’.
(1) Scan time calculation expression
Scan time is the sum of the processing time of scan program and interrupt program prepared by the user
and PLC internal time, and is distinguished by the following formula.
(a) Scan time = Scan program processing time ＋ Interrupt program processing time ＋ PLC internal
processing time
Scan program processing time = processing time of user program not saved as interrupt program
Interrupt program processing time = Sum of interrupt program proceeding time processed during 1 scan
PLC internal processing time = Self-diagnosis time ＋ I/O refresh time ＋ Internal data processing time
＋ Communication service processing time
(b) Scan time depends on whether to execute interrupt program and communication processing.
(2) Scan time monitor
(a) Scan time can be monitored 『Online』-『PLC Information』-『Performance』.
(b) Scan time is save in special relay (F) area as follows.
%FW50: max. value of scan time (unit: 0.1 ms)
%FW51: min. value of scan time (unit: 0.1 ms)
%FW52: current value of scan time (unit: 0.1 ms)
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