In modicon hot standby configuration,i want to setup redundant communication link to my scada through modbus ports.In case of failure of one link (means no switching system is still in Redundant mode without any problem) can i able to control through other link connected to Standby Controller.or i have to manipulate CHS command register.how it is possible with reasonable option

I'm guessing you have a Scada box with two serial ports, one connected to each processor.

At the Scada end, you'll have to tell it only to use one serial link at a time. Only write down the other link if the first fails. Tell it to talk to Node 1

At the Quantum end, set the PLCs to be node 1 and turn on bridging mode (you'll have to disconnect them from each other to set it up)

When you fire them up, the primary will always be node 1 and the standby will be node 32 (or is it 33, I can't remember off hand) and you will reach them by node number which ever serial port you are talking into.

You'll have to watch which port is in use when it comes to powering down a node, and might requre something to monitor the status of the spare link, and to force change over between the two links.

Easier way is Modbus Plus with a PCI-85 card. Because when the system switches standby/master, it moves the Modbus Plus address to the other CPU. So you would always talk to the same node number, and the system would switch it automatically when the CPUs swapped control.

Hi
In Quantum hostandby PLC I dont know what happen If the communication of Primary and standby fall even CPU of primary is running and controlling ( for example: the cable is cut out). for this situation whether Standby take over become Primary?
best regard

This topic has been dead since January 2007. You should open new topics, not dig up old ones.

What communication are you talking about? Communication to an external system like SCADA is not monitored by the hot standby system. If you are speaking of communication with the remote I/O network, an error in the network will cause the CPUs to switch. The PLC is monitoring its own health, and that includes remote I/O over the S908 coax network. But it has no way to tell if an external system stops communicating.