Rockwell Automation 1769-SDN Compact I/O DeviceNet Scanner Module User Manual - Manual (Page 145)

Publication 1769-UM009E-EN-P - August 2009 145
CompactLogix Backup on the DeviceNet Network Appendix B
• Unlike some backup systems (such as PLC-5 controller systems), the
primary controller still maintains control of the I/O, and switchover
does not occur if the primary controller is set to Program/Idle mode.
The secondary 1769-SDN scanner module also indicates that it is in Idle
mode.
• By default, a switchover will not occur if the default fault routine or user
fault routine is executed in the primary controller. However, the user
fault routine can force a switchover if desired.
• If an operator interface is on the DeviceNet network, it can work
without knowledge of which controller is primary or secondary.
• Online edits are not automatically performed on both primary and
secondary controllers, since no synchronization exists between primary
and secondary controllers. Once an online edit occurs on the primary
controller, the primary and secondary will have different programs.
• CompactLogix system backup on the DeviceNet network is not hot
backup. Hot backup implies complete synchronization of program,
program variables, and I/O. Also, I/O switchover is completely
bumpless with hot backup.