After implementing an 8-bit full adder, I decided to turn it into an 8-bit ALU. The ALU supports addition, subtraction, NOT, OR, and AND. It's considerably more complicated than the full-adder, but at the same time I'm happy with the degree of reuse I was able to achieve. The addition of support for AND, for example, required only the addition of a 2-1 mux per bit (2 74HCT157s for the whole ALU).
I've wired up two bits so far, and have started testing to ensure that the basics are sound before I turn it into even more of a rats nest. This turns out to have been a wise choice, as I made a few mistakes with the control bits -- mistakes which are much easier to correct with two bits than four.
I'll post schematics and diagrams when I get all eight bits done.
