The SN54AS181B and SN74AS181A arithmetic logic units (ALUs) / function generators have a complexity of 75 equivalent gates on a monolithic chip. These circuits perform 16 binary arithmetic operations on two 4-bit words as shown in Tables 1 and 2. These operations are selected by the four function-select (S0, S1, S2, and S3) lines and include addition, subtraction, decrement, and straight transfer. When performing arithmetic manipulations, the internal carries are enabled by applying a low-level voltage to the mode-control (M) input. A full carry look-ahead scheme is used to generate fast, simultaneous carry by means of two cascade (G and P) outputs for the four bits in the package.