I want to configure redundancy for CPU s7300 using software redundancy, module IM153-2 and 2 CPu. I have a question:

The rack use for module 153-2?

The IM153-2 module (only have quest change over from master to standby) OR (the master CPU control IM153-2 to control field deviece and when master failure IM153-2 change over master to standby then the standby cpu control IM153-2 to control field device)?

Thks

Process data from master is transferred to the slave (IM153-2) in the same network while data from standby CPU is discarded in assigned redundant slave.In case of switch-over, last valid data are locked by the redundant DP slave assigned by master and when the switch-over finishes, process data from new master is transferred to outputs.Read more in "4.1 How does a system with software redundancy work?' of the following manual:
http://support.automation.siemens.com/WW/view/en/1137637

I hope this helps,
Hamid Hosseini