Comms link failure

A recently added comms link from existing SLC5/03 to a Valmet XD DCS has failed when the PLC was powered down for the first time and then re-energised. The SLC5/03 has been fitted with a Prosoft Modbus card to accomodate the new link. The system had been working correctly up until the time of power loss. On re-energising, the PLC runs the process as it should but does not communicate to DCS. Two weeks later still waiting for some promised diagnostic software from engineer responsible for installation! Can anybody help please?
Regards Mike.

ps Understanding OK with ladder logic but rubbish with comms.

Do you have any method for resetting the communications from the Valmet end? A typical strategy when a Modbus master (the Valmet DCS) loses communications with the slave is for the slave to attempt to re-establish communications for a fixed number of tries and then stop trying. Another strategy is to wait for an increasing amount of time between attempts to re-establish comms, and quit when the time between retries exceeds somne duration. So it may be that the Valmet DCS has quit trying to communicate with the PLC.

It is also possible that the port on the PLC has reverted to a default configuration and the settings are different from what the DCS is using.

Thanks for replying Steve. A Valmet programmer confirmed that the DCS end of things is ok and problem lies with PLC. My gut feeling is that the PLC has as you suggested reverted to a default configuration. However without any hardcopy of previous configuration settings and communication configuration knowledge I will have to get the books out and start learning pretty fast.

Thanks again. Mike