Modbus TCP nodes in PM 902F
make use of on board two Modbus serial line, use third-party gateway modbus serial to tcp convertor and you can plug additional Modbus_TCP devices.
another option but I am not sure that works, would like to make test if anyone can try and check if that works...
Instead of configuring AC 900F as master configure it as Slave and let other devices be master and you can read values from Modbus master.
So in that case you will be having many master and one slave and question is multi master allowed on Modbus_tcp network ?
I have not tested practically, but by Modbus org seems multimaster supported.
Check this links, http://www.modbus.org/faq.php (Question : where modbus is used ? – it says multi master-slave)
Also check this http://www.modbus.org/docs/Modbus_Messaging_Implementation_Guide_V1_0b.pdf (On page 4/46 it shows network with many Modbus server(slave) and clients(master).