open project in GX
open parameter, I/O assignment, determine I/O address for this card
open parameter, Network param, MELSEC/Ethernet
under Module1 (if this is the first network card) make settings as needed, for example:
Network type - Ethernet
Starting I/O - that would be address of the module (first X or Y mapped to this card) such as 0 if it is in first slot etc. (assuming you are familiar with I/O mapping in mitsubishi).
Network number - 1 (this is arbitrary number you get to assign, each network on this plc must be unique).
Station number - 1 (must be UNIQUE for each node on particular network). in detail each node must:
a) use same network number (all nodes have "1" or "6" for network number)
b) use unique station number (each node is unique such as 1,2,3,21,25,26,37 etc.)
c) use unique IP and all IPs on same network must be valid for current subnet (should be obvious)
there are also some settings below those fields. note that each has specific text color. Text color has meaning, something like:
red - must not change
pink - can be changed etc.
