arduino nano pro rs485 breakout

I need to connect arduino nano pro as modbus rs485 slave.

I tried sketch with rs232 ftdi basic usb converter with pc such modbus master and work fine.

If I use rs485 breakout to connect arduino nano pro to rs485 it doesn’t work.

I connect the same pc modbus master with usb to rs485 to the rs485breakout but noting.

The pc modbus master and the usb to rs485 converter work fine, i trier with another modbus slave.

How do I connect arduino nano pro and rs485 breakout?

Thanks

Luca

I have a exactly the same problem with Mini Pro. Is there a solution?