Some RS485 shields are already available for the Raspberry Pi on the market, but these extensions are not suitable for professional use, because they come without a galvanic isolation between the RS485 bus and the Raspberry Pi. Without such isolation a damaging of the Raspberry Pi or malfunction of the device is possible, because of the large distances of a RS485 bus. Furthermore a full-duplex mode (RS422) is also not integrated.

The shield comes with a lot of additional features:

• RS485 mode (half duplex)
• RS422 mode (full duplex)
• galvanic isolation between Raspberry Pi and connected RS485 bus
• enhanced ESD protection
• adjustable automatic transceiver switching for RS485 mode
• adjustable control of transceiver/receiver via GPIO pin
• adjustable Pull-Up, Pull-Down und terminating resistors
• indicator LEDs for RX and TX 
• removable block terminal for bus connection
• many options adjustable via DIP switches

The RS485 is in use in many applications like:

• industrial and home automation (for example MODBUS)
• lighting control (DMX)
• maritime and navigation controls (NMEA0183)
• video surveillance (for example Pelco D)

If you like to know more about RS485 visit this website: http://www.radio-electronics.com/info/telecommunications_networks/rs485/rs-485-tutorial-basics.php