MKS Melzi and LCD2004 with rotary encoder kit.

I am trying to flash a Makerbase MKS Melzi board that came with a LCD2004 screen and rotary encoder.
I can get the LCD screen to work but not the encoder. I think that I may need special firmware for this as the LCD2004 normally comes with a keypad.
Can anyone point me in the right direction? I have Googled this to death!

there is a marlin lcd2004 file available in addition to marlin firmware also checkout
[marlinfw.org]