ALU logic breakdown part 1

Day 6

     The ALU is a combination of an adder/incrementer, left shift, and several Boolean logic functions. All of the possible functions are carried out simultaneously regardless of need and only the result that is desired is loaded onto the bus. This means that all of the logic functions can be carried out on just 2 relays per bit giving us the 4 outputs of the AND, OR, XOR, and NOT functions. The NOT function is carried out only on the B input but all others are carried out on the B&C inputs.  the adder/incrementer is also made up of only 2 relays and gives us a full adder with a dual rail carry in/out bit. The dual in/out carry bit allows for negation of the sum allowing the computer to work in negative numbers gives a vast improvement in flexibility. The add circuit can also be used by simply inputting a 1 to the carry line on the B input alone to increment should a simple count up be necessary. More to come Wednesday.