Finite State Machine (FSMs)
- An FSM is a sequential logic system with finite number of states
- Values stored in registers represent state of the circuit
- Two types of FSMs, Moore and Mealy FSMs
- Both have different output generation
Moore Machines
- Output is only function of state
Mealy Machines
- Output is function of state and inputs
Comparison of Mealy and Moore Machines
- Mealy machines tend to have less states
- Different outputs on arcs rather than states
- Moore machines are safer to use
- Outputs change at clock edge
Sequential Circuit Analysis
- In sequential circuit analysis, we turn a sequential circuit into a state table/state diagram
Example Circuit:
We can observed that Z = QQX from the diagram
- This means that the circuit is a Mealy machine
There are also four possible states QQ from two flip-flops
Finding the next states is harder:
- Find Boolean expressions for flip-flop inputs
- Use expressions to find actual flip-flop input values for each possible combination of present states and inputs
- Use flip-flop characteristic tables to find next states
Finally, we can fill out our state table:
From here, you can go on to make a state diagram to represent the table graphically