This should be a 4 bit ACU. It should take a 4 bit register A and a 4 bit register B and have the following functions Output register A (Output reg A) Output register B (Output reg B) ADD registers A & B Subtract registers A & B (A - B) | AND registers A & B OR registers A & B Compliment register B First you make a 1 bit ACU. This will be a 1 bit register with a 1 bit 8 to 1 mux. There are seven functions to implement. While the order of the functions is up to you: make function zero (000) be "no change" Now you are going to take a D type flip-flop and put an 8 to 1 mux in front of it. You only need 7 of the inputs for new functions, so you have one left over to feed back the output into the input. In this circuit, if "M" is a zero, the circuit adds and if it is one, it subtracts. If you select the right two adjacent inputs on the mux, then you can use the S0 on the MUX input to also control subtract switch. In the circuit above, when MUX "two" is selected (010) S0 is zero, so the circuit subtracts. When "three" is selected (011) SO is one, so the circuit subtracts. You do realize the above circuit is for Bit zero, and that in bits 1 through 3, the "carry in" must come from the "carry out" of the level below it. It is obvious that each level of the A register must go to the inputs for functions "Output register A" and the circuitry for "ADD registers A & B", "AND registers A & B" and "OR registers A & B" While each level of register B must go to "Output register B" and the circuitry for "ADD registers A & B", "AND registers A & B" "OR registers A & B" and "Compliment register B" having made a 1 bit ACU stack up 4 of them of make a 4 bit ACU. You must connect the two registers (A & B) to the various bit levels of the ACU. You do have to consider how to hook up the Adder Subtract or circuits. The "S" or sum output will go to the mux on that level, and the "carry out" will go to the "carry in" on the next level. What do you need to report out? You need a 1 bit ACU This ACU will have three controls S2, S1 and S0 It will have two inputs A and B. It will also have one output O. You will also need a 4 bit ACU. This ACU will have three controls S2, S1 and S0 It will have eight inputs A3, A2, A1, A0, B3, B2, B1 and B0 It will also have four outputs O3, O2, O1 and O0. This should be a 4 bit ACU. It should take a 4 bit register A and a 4 bit register B and have the following functions Output register A (Output reg A) Output register B (Output reg B) ADD registers A & B Subtract registers A & B (A - B) | AND registers A & B OR registers A & B Compliment register B First you make a 1 bit ACU. This will be a 1 bit register with a 1 bit 8 to 1 mux. There are seven functions to implement. While the order of the functions is up to you: make function zero (000) be "no change" Now you are going to take a D type flip-flop and put an 8 to 1 mux in front of it. You only need 7 of the inputs for new functions, so you have one left over to feed back the output into the input. In this circuit, if "M" is a zero, the circuit adds and if it is one, it subtracts. If you select the right two adjacent inputs on the mux, then you can use the S0 on the MUX input to also control subtract switch. In the circuit above, when MUX "two" is selected (010) S0 is zero, so the circuit subtracts. When "three" is selected (011) SO is one, so the circuit subtracts. You do realize the above circuit is for Bit zero, and that in bits 1 through 3, the "carry in" must come from the "carry out" of the level below it. It is obvious that each level of the A register must go to the inputs for functions "Output register A" and the circuitry for "ADD registers A & B", "AND registers A & B" and "OR registers A & B" While each level of register B must go to "Output register B" and the circuitry for "ADD registers A & B", "AND registers A & B" "OR registers A & B" and "Compliment register B" having made a 1 bit ACU stack up 4 of them of make a 4 bit ACU. You must connect the two registers (A & B) to the various bit levels of the ACU. You do have to consider how to hook up the Adder Subtract or circuits. The "S" or sum output will go to the mux on that level, and the "carry out" will go to the "carry in" on the next level. What do you need to report out? You need a 1 bit ACU This ACU will have three controls S2, S1 and S0 It will have two inputs A and B. It will also have one output O. You will also need a 4 bit ACU. This ACU will have three controls S2, S1 and S0 It will have eight inputs A3, A2, A1, A0, B3, B2, B1 and B0 It will also have four outputs O3, O2, O1 and O0