A project log for 4 bit TTL ALU

Alternative for the 74LS181 ALU, built in One Square Inch

roelhroelh 08/16/2018 at 17:260 Comments

The circuit description, as given in the first log entry, does not provide subtraction. 

This was added by simply putting four exclusive-or-gates in the lines for the A inputs. 

The function input F0 is now used to control these exor gates, and is no longer connected to the multiplexers. These inputs of the multiplexer are connected to logic zero. They were used for negating the B input, but negating an input can now be done with the new exor gates.