Almost done, but got stuck with register problems, which ones will be source and destiny of instructions.

In case of ALU there are two sources. And to make things worse, the two inputs of the 74LS181 ALU haven't same powers, the A input has a lot more functions allowed.

It's easy to permit all registers to work in all roles in a software simulator like Logisim, but when it comes to use real chips it becomes a nightmare due to the huge quantity of controlled 3-state buffers (74LS244) required to control the data flow.