Sequential Circuit Analysis

Tom Kelliher, CS 220

Mar. 31, 2006

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Assignment

Read 6-5.

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:

\begin{figure}\centering\includegraphics[]{Figures/seqCkt.eps}\end{figure}

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.

Present State I Next State O
0 0 0 1
0 1 1 0
1 0 1 0
1 1 0 1

State Diagrams

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

State diagram for our example (Mealy):

\begin{figure}\centering\includegraphics[]{Figures/seqCktDia.eps}\end{figure}

How do I read this?

Moore machine example:

\begin{figure}\centering\includegraphics[]{Figures/moore.eps}\end{figure}

Example

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

\begin{figure}\centering\includegraphics[]{Figures/seqExmpl.eps}\end{figure}

Is this Mealy or Moore?


Thomas P. Kelliher 2006-03-30
Tom Kelliher