Hardware Reference
In-Depth Information
Figure 5.1
State machine categories (from a hardware perspective).
state machines. The two fundamental decisions before starting a design are then the
following:
1) Decide the state machine category (regular, timed, or recursive).
2) Next, decide the state machine type (Moore or Mealy).
It is important to recall, however, that regardless of the machine category and type,
the state transition diagram must fuli ll three fundamental requisites (seen in section
1.3):
1) It must include all possible system states.
2) All state transition conditions must be specii ed (unless a transition is uncondi-
tional) and must be truly complementary.
3) The list of outputs must be exactly the same in all states (standard architecture).
5.2 Architectures for Regular (Category 1) Machines
The architectures for category 1 machines are summarized in i gure 5.2. These repre-
sentations follow the style of i gures 3.1b,d, but the style of i gures 3.1a,c could be
used equivalently. The output register (i gure 5.2c) is optional. The four possible con-
structions, listed in i gure 5.2d, are summarized below.
Regular Moore machine
(i gure 5.2a): In this case, the input (if it exists) is connected
only to the logic block for the next state. Consequently, the output depends only on
the state in which the machine is (in other words, for each state, the output value in
unique), resulting a synchronous behavior (see details in section 3.5). Because modern
designs are generally synchronous, this implementation is preferred whenever the
application permits.
