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System Startup
The following actions occur during orderly startup of the GMR system:
1.Each PLC disables its outputs to Genius blocks. If the Outputs Disable function does not complete successfully, the GMR software sets the flag ªGMR System Initialization Faultº and the GMR software puts the PLC in Halt mode.
2.Each PLC determines its PLC identity: PLC A, PLC B, or PLC C.
For a PLC, all bus controllers that have been included in the GMR software configuration must have been assigned the same serial bus address: 29, 30, or 31. Each PLC checks its GMR configuration to be sure this has been done. If it has, the PLC determines its identity as follows:
PLC A | all GMR bus controllers at serial bus address 31. |
PLC B | all GMR bus controllers at serial bus address 30. |
PLC C | all GMR bus controllers at serial bus address 29. |
If a PLC determines that its GMR bus controllers have been configured with differing serial bus addresses, or with addresses outside the range 29±31, it logs an ªInvalid Bus Addressº fault into its PLC Fault Table and stops the PLC.
3.Each PLC checks the online status of the other PLCs. ªOnlineº means the other PLC is running its application program, and its outputs are enabled.
4.Each PLC compares its initial program checksum with those of the other PLCs. If they do not match, the PLC may (as configured) either stop or keep running. The next table compares the effects of checksum mismatches with the PLC configured to allow or reject online program changes:
5.Each PLC compares its initial GMR configuration checksum with those of the other PLCs. If they do not match, the PLC stops.
After successful initialization, when the application program is running, the PLC will continuously compare its program checksum against the initial program checksum, and if they do not match, the PLC will (as configured) either stop or keep running.
Note that if a synchronizing PLC detects that an online PLC has gone offline during synchronization, it attempts to restart data synchronization with the other PLC. If the other PLC is not online, the synchronizing PLC will flag that synchronization is not possible, and halt.
6.PLC C (which uses serial bus address 29) sends an ªAssignControllerº datagram to all blocks and also sends an ªAssignMonitorº datagram to the blocks configured for Hot Standby mode to ensure correct operation with three PLCs. If this function does not complete successfully, the GMR software places a ªGMR System Initializationº fault into the PLC Fault Table. This fault can be configured to stop initialization and halt the PLC or allow it to continue.
7.(PLC B or PLC C) initializes data values. This is described in more detail on page
8.The Inhibit bit is released, allowing the PLCs to start executing the application program.
9.When the Continue control flag is set by the user's application program, the PLC begins sending outputs computed by the application program to Genius blocks.
10.If these outputs match the current output states of the blocks, they are accepted by the blocks. If a block detects that outputs from a PLC do not match the current
GeniustModular Redundancy Flexible Triple Modular Redundant (TMR) System | ||
| User's Manual ± March 1995 |
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