Because there are two links (Copro and RIO) between the Primary and Standby PLCs, if a PLC detects an error on one link, it still has a link available to send diagnostic information to the other PLC.
Generating and Sending Health Messages
The Quantum Hot Standby modules exchange a health message approximately every 10 ms.
If the Primary CPU becomes inoperative, the Standby CPU is notified and assumes the Primary CPU role.
However, if the Standby CPU becomes inoperative, the Primary CPU continues to operate as a standalone CPU.
The RIO head modules periodically verify communication with one another.
The Primary CPU sends a health message to the Standby CPU either:
If the Standby CPU never receives any message on either of these links (Copro, S908 RIO, or Quantum Ethernet RIO), the Standby CPU tries to determine the cause and assumes control if necessary.
If the Primary CPU does not receive a valid response from the Standby CPU, the Primary CPU operates as a standalone CPU.
The system automatically performs startup confidence testing on the Quantum Hot Standby Copro that attempt to detect hardware errors in the Copro before the application is allowed to run.
If the Copro does not pass the tests, the Standby PLC remains offline and does not communicate with the other Quantum Hot Standby modules.
Conducting Run Time Tests
The system automatically performs run time tests whenever the Copro is in the operational state.
NOTE: Run time tests are executed in small slices to prevent delays in scan time.
If the Copro does not pass the tests, the Standby PLC remains offline and does not communicate with the other Quantum Hot Standby modules.
