For Nano-10 you can only recover the IP address using the TLServer and U-485 adapter connected to the PLC via the RS485 port.
You need to run TLServer and test the RS485 communication with the PLC first. If for some reason your PLC has changed the serial port settings you may encounter some difficulties connecting to it. If so, then put the jumper on J4 to pause the PLC, then power cycle it so that it starts up in default 38400,8,1,n. You can test the communication with the PLC via the "Setup Serial Port" screen. Please refer to the manual for details.
Your i-TRiLOGI software will connect to the local host (IP address 127.0.0.1:9080) and then you will be able to retrieve the IP address, subnet mask, Internet gateway etc to allow you to connect to the PLC via its IP address.
For Fx PLCs, as well as FMD PLCs with newer firmwares you can put the PLC into a default IP address of 192.168.1.15 (note that it is ".15", not ".5" when you power on the PLC with DIP switch #3 set to ON. That allows you to retrieve PLC's settings via Ethernet port using the known IP address. Do remember to turn OFF DIP switch #3 and power-cycle the PLC after you have made changes and want to connect to the IP address defined in the PLC.
