Keep in mind that this particular format can vary from one microprogrammed design to the next, and is a function of how one chooses to do the design. Each microinstruction explicitly contains the settings of each of the control signals in the datapath. All other signals, most importantly the Load signals and the MemWrite and the RegWrite signals must all be deasserted. Each microinstruction also contains bits to indicate where the next microinstruction resides. In the case of our LC-2 microprogrammed controller, we've provided two targets for each microinstruction.
Most states require only one target.
Some states require two. The microinstruction provides a way to explicitly encode both target states. There are also three bits to help determine when target0 should be the next state and when target1 should be the next state. This selection be based on the Ready bit or the Condition of a branch instruction. The logic diagram of the logic that sequences from one microinstruction to the next is provided below.