Rockwell-automation 1769-SDN Compact I/O DeviceNet Scanner Module User Manual de usuario descargar pdf (Pagina 130)

130 Publication 1769-UM009E-EN-P - August 2009

Appendix B CompactLogix Backup on the DeviceNet Network

How the Backup Works

The following figure shows an example backup system. In the backup system,

the following occurs:

• Both controllers/scanners simultaneously receive all inputs.

• Both controllers execute in parallel but are not synchronized.

• Only the primary controllers send output data to the I/O devices. A

virtual switch in the 1769-SDN scanner module is used to switch

outputs between primary and secondary controllers.

• After failure or forced switchover, outputs are automatically switched by

the 1769-SDN scanner module from the primary controller to

secondary. When the switch occurs, the secondary controller becomes

the primary controller.

The switchover occurs so quickly that the I/O devices do not timeout;

these devices are unaware that redundant controllers/scanners exist and

are unaware of the switchover.

Primary Controller

Secondary Controller

Primary Scanner Module

Secondary Scanner Module

DeviceNet Network

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Rockwell-automation 1769-SDN Compact I/O DeviceNet Scanner Module User Manual de usuario Pagina 130