The design of the control unit begins with block diagram of the computer, which we have seen many times (see Chapter 7, section 1). Then we define the instructions. Finally, we write out a sequence of signals that will implement each instruction in terms of all the wires in the block diagram. That is what this first file is...

Once we have this list of signals, we need to rewrite it as a DFA with states. This is the following file...

The above DFA is not quite usable yet because the values of the non-state wires are not determined. They have to be set as a combination of other signal wires, and states. So we go through the dfa and collection together all references of the same wire and either OR or AND them together. Usually we OR them, but in some cases, we need to AND them with other signals, especially those emanating from the ALU. The following is the result...