Synchronous state machines. Moore and Mealy state machines (FSM)
A synchronous state machine is a machine whose transition between states occurs on the triggering edge of a clock signal. There are two types of synchronous finite state machines: Moore and Mealy machines. A Moore machine's output is solely dependent on its current state, while a Mealy machine's output depends on both its current state and current inputs. Moore machines are generally faster and easier to compose than Mealy machines. Mealy machines can have a lower response time but require more clock cycles to change state and are more expensive to produce when the number of possible states grows large. Both Moore and Mealy state machines are important concepts in digital design that can be used to model algorithms or processes simply or complexly.
Synchronous state machines. Moore and Mealy state machines (FSM)
- 2. A synchronous state machine is a machine whose transition is controlled by the state signal and occur on the triggering edge of the clock A finite state machine is a machine that has many states and has a logical way of changing from one state to the other under guiding rules. Two types of synchronous finite state machines to be discussed are Moore and Mealy state machines
- 3. A Moore state machine is a machine whose output values are solely dependant on the current state of the machine A Mealy machine on the other hand is a state machine whose output values are determined by the current state and the current inputs of the machine
- 4. The state of a Moore state machine is determined by the state of the machine In the diagram below, the state is determined by the state of the JK and D flip- flops
- 5. Below is the state table for the Moore state machine on the previous page As seen below, the state of the machine is determined by the state of the machine only
- 6. The output depends on the current state and the input In the diagram below, the output Z will be determined by the input X and the state of the machine
- 7. As seen below, the output of the mealy state machine are determined by the inputs and the current state of the machine
- 8. The Mealy state machine’s state is changed by the inputs and the state of the machine but The Moore state machine’s state is affected by the state of the machine only Moore machines are slower than the Mealy machines Moore machines are easier to compose than Mealy machines The Moore state machine takes at least one clock cycle to change the state of the machine while the Mealy state machine is guaranteed to use more than one clock cycle
- 9. Moore machines are cheap They are easy to use Moore state machines are very fast Mealy machines are reactive i.e. they have a low response time (they are fast)
- 10. Mealy state machines are expensive to produce Number of states can become unmanageable (they become too many)
- 11. Mealy state machines are used in processors due to their property of having many states Mealy state machines are also used to provide a rudimentary mathematical model for cipher machines A Moore state machine is used as a right enable in SRAM because of its speed. It is used in SRAM because SRAM needs a level-sensitive control (signal has to be asserted for an amount of time)
- 12. In conclusion, Mealy and Moore state machines are very important concepts in digital design These state machine can be used in the design of mathematical algorithms Mealy and Moore state machines can come in both simple (having one input and output) to complex (having many inputs and outputs) types