Rockwell-automation 1794-L34 FlexLogix Controller System User Manual Manuel d'utilisateur télécharger pdf (Page 104)

Publication 1794-UM001G-EN-P - January 2007

104 FlexLogix Back-Up on DeviceNet

How the Back-up Works

Figure shows an example back-up system. In the back-up system, the

following occurs:

• Both controllers/scanners simultaneously receive all inputs.

• Both controllers execute in parallel but are NOT synchronized.

• Only the primary controllers sends output data to the I/O

devices. A virtual switch in the 1788-DNBO cards is used to

switch outputs between primary and secondary controllers.

• After failure or forced switchover, outputs are automatically

switched by the 1788-DNBO card 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.

43493

DeviceNet

Primary controller

Secondary controller

All backed up devices must

operate on DeviceNet

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Rockwell-automation 1794-L34 FlexLogix Controller System User Manual Manuel d'utilisateur Page 104