Sequential Circuit Analysis

Tom Kelliher, CS 220

Oct. 31, 2003

Administrivia

Announcements

Homework problems 1--4 and VHDL sketch of 6 due Monday. 5 and 6 due Friday.

Assignment

For Monday read 4-5,6.

From Last Time

Flip-Flops and waveforms.

Outline

1. Reverse engineering a sequential circuit.

2. Input equations, state tables, and state diagrams.

3. Example problems.

Coming Up

Sequential circuit design.

Reverse Engineering Sequential Circuits

Analysis = reverse engineering.

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

Input Equations, State Tables, and State Diagrams

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.

Input Equations

What are the equations for O and D (input equation)?

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

State Tables

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

1. Present state inputs --- flip-flop outputs.

2. Next state outputs --- derived from input equations for flip-flops.

State Diagrams

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

State diagram for our example (Mealy):

How do I read this?

Moore machine example:

Example

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

Is this Mealy or Moore?