Chapter 4 (pp. 194-202), Chapter 8 (pp. 413-432), Chapter 9 (pp. 449-455 and 460-470), and Chapter 10 (pp. 498-524) of the Katz text.
To be able to tri-state an output, you'll need to use the ABEL .OE suffix. Writing Areg.OE = EnaA; in your EQUATIONS is all you need to do if Areg is aliased to the 8 flip-flops in your A register (e.g., Areg = [A7..A0];).
Turn in your ABEL and/or schematic files along with simulation waveforms that show in consecutive cycles: the value 7 being loaded into the B register, the value in B transferred to the register A while a new value of 1 is loaded into B, the ALU performing the "A+B" operation and placing the result in A, clear the value of A to 0.
Turn in your ABEL file and waveforms for the two situations described above. Also include a rationale for why you picked the state encoding you used.