Interfacing STRATIX 3 FPGA with RS485 and RS232.

You can either short the ~RE and DE to ground and vcc respectively if you want the transceiver to be always enabled, or connect those pins to the FPGA if you want to be able to turn the transceiver on and off.

If you plan to use the MAX485 then you will need a level converter between the MAX485 and the FPGA, as the MAX requires a 5V supply but the FPGA can only have input/outputs at up to 3.3V. I would suggest to use the MAX3485 instead, that can operate at 3.3V and can be directly connected to the FPGA without level translation.