CyberCertPrepOT Security FundamentalsOT Fundamentals: Network Architecture & ProtocolsMEDIUMFree question
A SCADA master polls register 40001 and receives a reply with function code 0x83 and exception code 02. What happened?
- A.A write to a coil was refused with a server device failure code
- B.A read of holding registers failed with illegal data address
- C.A diagnostic request returned an illegal function exception code
- D.A holding register read succeeded after a retry delay
Why B is correct
An exception reply sets the high bit of the request function code, so 0x83 answers function 3 (read holding registers). Exception code 02 is illegal data address, meaning the register is not in the device map.
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