The Arithmetic Logic Unit, or ALU, generates all the grayscale pixel values that are need by the various graphics algorithms that are performed by the GP256. To do this, the ALU works in conjunction with a set of three registers and it controlled by the Main PLA Controller.

In the design and implementation of the ALU, first all the operations that the ALU had to perform needed to be considered. Then, the ALU had to be designed to fit in a minimum amount of space. Finally, the ALU had to be tested to make sure that every operation performed correctly.