Encoder Programming

Hey everyone,

I have a 32 bit encoder. Can some one explain this part of the program. What i know is that you have the convert gray to binary which is nothin but XOR. That is XOR of grey is binary. But i dont know what is happening here. Also I how does the resetting of encoder works. I mean how to do program.
http://dl.dropbox.com/u/6582607/Encoder.JPG

Grey Code
Look at http://www.plcdev.com/using_ladder_logic_for_gray_code_conversion

Encoder value does not reset just where you start the position from does

Also for more assistance provide PLC Model and Encoder Model

Thanks Micheal. I am aware of converting gray code to binary but i didnt get the part where is adding and negating. PLC is Controllogix and encoder is TWk.

I don't believe that it is converting Gray to binary. It is trying to deal with the high bit of the low 16 bit word being interpreted as a negative indicator and messing up the math.