16.4 ONE-HOT PROGRAMMABLE ASYNCHRONOUS SEQUENCERS 835
Of course, the one major drawback to MAC module FSM design is the fact that each
state-to-state transition must involve one, and only one, state variable change. Thus, the
controller state machine must be composed of an even number of states that are unit-
distance coded. When this is not the case, the logical adjacency requirement must be met by
either adding buffer states or by increasing the number of state variables. Adding a buffer
state may or may not be acceptable, since it does introduce a delay in executing a given
transition. Adding state variables may require increasing the size (capacity) of the MAC
module. As an example, the vending machine controller in Fig. P13.2 would require