**Tom Kelliher, CS 240**

**Apr. 7, 2010**

Xilinx assignment due Friday.

Exam on 4/14, covering 4.1-5.2, including material covered in class on addition.

Read 5-5.

Flip-Flops and waveforms.

- Reverse engineering a sequential circuit.
- Input equations, state tables, and state diagrams.
- Example problems.

Sequential circuit design.

Analysis = reverse engineering.

One doesn't ordinarily do this, but doing so will help with sequential circuit design.

Consider the following sequential circuit:

What does it do -- high level?

What happens if we use !Q as the input to the NEXOR rather than Q?

Mealy (this circuit) vs. Moore machines.

What are the equations for `O`

and `D`

(input equation)?

Do these differ that much from anything we've already seen?

State tables are similar to truth tables, with two additions:

- Present state inputs -- flip-flop outputs.
- Next state outputs -- derived from input equations for flip-flops.

Present State |
I |
Next State |
O |

0 | 0 | 0 | 1 |

0 | 1 | 1 | 0 |

1 | 0 | 1 | 0 |

1 | 1 | 0 | 1 |

Conveys same information as state table, in a visual form.

State diagram for our example (Mealy):

How do I read this?

Moore machine example:

Determine input and output equations, state table, and state diagram for this circuit:

Is this Mealy or Moore?

Thomas P. Kelliher 2010-04-06 Tom Kelliher