Thank you very much for the help. Now it is very clear to me, all the configurations,communication methods and the modbus commands.
For your info, we are using our own RS232 to RS485 converter. In this we are using SN75176 from TI for the RS485 convertion. In this chip, pin number 6 is used for " A " and pin number 7 is used for "B". That is the same we have connected to multirangers A and B terminals. We have made two of this dongle and tested sending and receiving data across, it worked fine.
But as you said if the naming convetions are not standardisd then there could be communication problem because of this.
-> So one of my check is, swaping the terminals and test.
Thank you very much for suggesting the ModScan32 tool. It is very useful for our testing.