The PLC and the I/O modules on the S908 network are programmed and maintained through Control Expert. You can perform all operations (configuration, tuning, diagnostics, etc.) on the 140CRA31908 module, 140CRP93•00, or Quantum S908 remote drops from the PC on which the Control Expert application is downloaded.
Use the Control Expert application to download the 140CRA31908 module and 140CRP93•00 module configurations together.
You can replace these modules with identical modules. In each case, the replacement module gets the previous configuration and parameters automatically during the initialization of the CPU:
The S908 I/O network characteristics are the same as those for Quantum 140CRP93•00 modules:
-
You can manage a maximum of 31 SY/MAX, Quantum, and 800 Series I/O remote drops.
-
Each remote drop supports up to 64 words IN and 64 words OUT.
-
Use only the state RAM mode to program the I/O modules over the S908 network. (The Device DDT programming mode is not supported; topological I/O addressing is supported.)
-
I/O data is exchanged only when the CPU is running.
-
You can configure only one S908 network. It can be a
redundant network if you configure two 140CRA31908 modules and a 140CRP93•00 that corresponds to each.
-
I/O data over S908 is processed only on the MAST task to create a deterministic network. The 140CRA31908 module, therefore, supports only the MAST task (even for modules that are configured on its local rack).
NOTE: LL984 section and segment schedulers are not supported for the 140CRA31908 module.
Impact of the S908 Network on the Redundant Operating Mode
The support of a redundant S908 network has no impact on
redundant M580 architectures. The management of the I/O redundancy over the S908 network is independent of redundant operating modes. Therefore, a loss of communications on the S908 network does not drive a M580 CPU switchover.
The redundant system performs a CPU switchover only when these conditions are all met:
In a mixed configuration that includes two 140CRA31908 modules and at least one Ethernet CRA module, the CPU switchover is performed only if the primary CPU loses its EtherNet/IP connection to all Ethernet CRA modules and both 140CRA31908 modules.
The user can force a CPU switchover with the swap bit in the redundant DDT (where QSA represents the 140CRA31908 module):
IF (Remote IO Health for QSA1 == 0) AND (Remote IO Health for QSA2 == 0) THEN HSBY_DDT.swap = 1
NOTE: The RIO health is part of the 140CRA31908
module diagnostics provided by the 140CRA31908 DDT.
Impact of the Redundant Operating Mode on the 140CRA31908
During a CPU switchover, the 140CRA31908 module behaves like the 140CRA31200 module. Within the remote drop
hold up time, the 140CRA31908 keeps communicating with the modules on its local rack. The values are read from the input modules and copied to the memory of the 140CRA31908 module. The last output values received by the 140CRA31908 from the CPU are sent to the output modules that are configured on its local rack or on the S908 network. This mechanism maintains the current values of the outputs during the CPU switchover.
Impact of Power Cycle on the 140CRA31908 Module Redundancy
After switchover triggered by power cycle on the 140CRA31908 module, the redundancy is effective 40 s after the power up.
Switchover considerations:
-
The 140CRA31908 module is the master of the I/O points during the switchover. The switchover is bumpless on the S908 RIO.
-
The S908 RIOs are not refreshed during two PLC scans when the switchover follows a command, stop, halt, or loss of communications to the primary PLC.
-
The S908 RIOs are not refreshed during four PLC scans when the switchover follows a loss of communications to all Ethernet CRA modules.
