CyberCertPrepOT Security FundamentalsOT Fundamentals: ICS/SCADA BasicsEASYFree question
A trainee asks about the order of steps in one PLC scan cycle. Which sequence is correct?
- A.Read inputs then run the logic then write outputs
- B.Run the logic then read inputs then write the outputs
- C.Write outputs then read inputs then run the logic once
- D.Poll the historian then run the logic then reset the CPU
Why A is correct
A scan samples the physical inputs into an image table, solves the program using that snapshot and then updates the physical outputs. Running logic before reading inputs would act on stale data and a PLC does not poll a historian.
Know someone studying for OT Security Fundamentals? Send them this one.