State Industries GFK-0827 manual Data Transfer from Backup Unit to Active Unit

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The transfer of the redundancy data during each sweep will be in blocks with each block checked for data integrity. The transferred data will be held in a temporary area by the backup CPU until all data has been received and verified from the active unit. Then the backup CPU will copy that data from the temporary area to the actual PLC memories. The transfer is capable of being performed on either RCM link. If one RCM link fails then the transfer will switch to the other RCM without causing a loss of synchronization in the system. If at any time during a transfer the active unit fails or the full transfer fails to complete properly (both RCMs fail) then the backup unit will disregard the data that has been transferred to the temporary area and proceed with the values it already obtained during its input scan.

The last part of the input data transfer is the synchronizing message containing the ºStart of Sweep Timeº. The ºStart of Sweep Timeº is the universal start of sweep time for the redundancy system. Normally each PLC CPU operates its elapsed time clock on which timers are based independently and the clocks are always started over from zero on a power cycle. Two independent clocks would cause time discontinuity at switch over time. In addition the clocks will tend to drift from each other over time. The redundancy system corrects for this by keeping a single elapsed time value for the entire redundancy system. The time will be continuous as long as one of the two systems continue to run and the active unit will continuously pass the time to backup unit to correct for any natural drift in the clocks. When a switch over occurs, the same time will continue to be kept in the new active unit.

Data Transfer from Backup Unit to Active Unit

Eight bytes (4 registers) of data can be transferred from the backup unit to the active unit during the input data transfer before the logic solution. To initiate this transfer, the backup unit executes SVCREQ #27 (Write to Reverse Transfer Area) to copy eight bytes of data from the reference specified by PARM to a temporary buffer (SVCREQ #27 on the active unit will have no effect). This transferred data will be stored in a temporary buffer on the active unit.

In the active unit, SVCREQ #28 (Read from Reverse Transfer Area) is then executed to copy the eight bytes of data from the temporary buffer to the reference specified by PARM (SVCREQ #28 will have no effect on the backup unit).

Note

There is always a one sweep delay between sending data to the active unit using SVCREQ #27 and reading the data using SVCREQ #28 on the active unit.

This data copied from the buffer is not valid

Hduring the first scan after either unit has transitioned to RUN;

Hwhile the backup unit is in STOP mode;

Hif the remote unit does not issue a service request to the sending unit.

An example of this data transfer is described below.

This data should not be used if REM_RDY is off or if REM_RDY is transitioning to on.

If the following two rungs are placed in the program logic of both units, the backup unit will send %P0001 through %P0004 to the active unit. The active unit will read the data into %P0005 through %P0008. %P0001 through %P0004 on the active unit and %P0005

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Series 90-70 Hot Standby CPU Redundancy User's Guide ± December 1993

GFK-0827

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Contents GE Fanuc Automation GFL±002 Related Publications Content of this ManualWe Welcome Your Comments and Suggestions PrefaceContents Chapter System Components Chapter Configuration Chapter Operation System Operation Fault Detection and Control Actions Synchronized Hot Standby CPU Redundancy System Configuration Contents Hot Standby CPU Redundancy Product Chapter IntroductionGFK-0827 Benefits of the Hot Standby CPU Redundancy Product Features of the Hot Standby CPU Redundancy ProductCable Connections Systems for Hot Standby CPU Redundancy SystemsGenius I/O System Local I/O SystemControl Strategy Basic Hot Standby OperationSynchronized Hot Standby CPU Redundancy System Configuration Redundancy Communications Module Redundancy CPU ModuleEffect on Scan Time Bumpless SwitchingSwitch to Backup Unit Time Synchronized CPUsOn-Line Repair Configurable Backup Data SizeOn-Line Programming Programming Considerations Configuration RequirementsTerm Definition Definition of TermsAcronym Definition Commonly Used AcronymsRedundancy CPU Chapter System ComponentsCapacities for Redundancy CPU, IC697CPU780 Watchdog TimerCPU Architecture Redundancy CPU IC697CPU CPU FeaturesValid Operating Mode Selection CPU Mode SwitchCPU Status LEDs Memor y Protect KeyswitchBattery Connectors Expansion Memory Boards for CPU Serial Port ConnectorExpansion Memory Board Redundancy Communications Module RCM FeaturesBoard OK RCM System Status LedsUnit Selection Pushbutton RCM ConnectorsBus Transmitter Module LED Status IndicatorsBus Receiver Module BTM ConnectorsGenius Bus Controller Bus Signal TerminationBRM Connectors Genius Bus Controller User Features Racks GBC ConnectorsConfiguring a Hot Standby CPU Redundancy System Chapter ConfigurationRedundancy System Requirements Basic Redundancy System SetupLogicmaster 90 Configuration System ConfigurationMonitor or Online mode Screens for Fault Category ConfigurationHandling Folders Configuration with LogicmasterConfiguration of a Redundancy CPU Module GFK-0827 Redundant CPU Requirements Background Window Normal Sweep ModeRedund Type Constant Sweep Mode Constant Window Sweep ModeShared I/O Ctrl StrgyFail Wait Shared I/O Reference Values Shared I/O Data ParametersReference Type ReferenceSize CalculationforNumberofBytes Transfer Data SizeConfiguring a CPU Expansion Memory Board Configuration of a Redundancy Communications Module Configuration Paired GBC Parameter Configuration of a Genius Bus ControllerSerial Bus Address Configuring a Primary Redundant PLC Select the Redundancy CPU Module Select an Expansion Memory Board Configure the Redundant Communications Module Configure a Genius Bus Controller Configuration Configure Genius I/O Blocks Configure the Bus Transmitter Module Configuring a Secondary Redundant PLC Change Redund Type GFK-0827 Chapter Operation Power-Up Sequence of a Redundant CPUIncompatible Configurations Resynchronization of the Redundant CPU Hot-Standby Redundancy Control Strategy First Data Transfer %I, %AI and Synchronization Synchronous ScanData Transfer from Backup Unit to Active Unit Second Data Transfer %Q, %AQ, %R, and %M Switching Control to Backup UnitRole Switch Svcreq Definition for% S Reference for Redundancy Status References for CPU RedundancyRedundancy CPU Considerations Differences in Operation for CPU RUN Disabled ModeRUN/ENABLED Locrdy Locact Remrdy Remact Configuration of Fault Actions Background Window Time Stop to RUN Mode TransitionWords per Sweep = Ovrpre %S Reference Timed ContactsGenius Bus Controller Switching Fault Categories Fault DetectionChanging Fault Category Actions Fault Zoom Help Text for Redundancy Error Codes PLC Fault TableFaulting RCMs, Losing Links, and Terminating Communications GFK-0827 Maskable Fault Group Descriptions Fault Actions in a CPU Redundancy SystemUserConfigurable Maskable Fault Group ActionsNon-Maskable Fault Action Descriptions Non-Maskable Fault Group DescriptionsOn-Line Repair Recommendations On-Line RepairMaintaining Parallel Bus Termination Redundancy Communications Module and Cables Power SupplyRacks Central Processor UnitGenius Bus Controller Redundancy Communications Link FailuresBus Transmitter Module GeniusBlocks Genius BusRedundancy Alternatives Appendix Redundancy AlternativesRedundancy Option Key See Table PLC RedundancyOptionsSeries 90-70 Redundancy Through Application Logic Index Index Index Index Index