Sequential Circuit Design:Sequential Circuit Design: Practice
9/15/09 - L21 Sequential Circuit Analaysis Copyright 2009 - Joanne DeGroat, ECE, OSU1 Sequential...
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Transcript of 9/15/09 - L21 Sequential Circuit Analaysis Copyright 2009 - Joanne DeGroat, ECE, OSU1 Sequential...
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9/15/09 - L21 Sequential Circuit Analaysis
Copyright 2009 - Joanne DeGroat, ECE, OSU 1
Sequential Circuit Analysis
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9/15/09 - L21 Sequential Circuit Analaysis
Copyright 2009 - Joanne DeGroat, ECE, OSU 2
Class 21-Sequential Circuit Analysis Design of a simple sequential circuit Analysis of an existing circuit
Material from section 5-4 of text +
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State machine synthesis Creation of state machine State machines are digital sequential circuits
that transition through a series of states according to their design.
For the creation of any such circuit always start with the problem definition or the circuit specification.
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Problem Statement Design a 2 bit up counter that has no preset state
and continually cycles thought the 4 states. This can be defined by a table –
called a state table. Present State Next State 00 01 01 10 10 11 11 00
9/15/09 - L21 Sequential Circuit Analaysis
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A diagram representation This form is termed a state diagram
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Sequential circuits Basic form and elements
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This problem Storage Elements
– 2 Flip-flops No inputs Current state is the
output Combination logic
generate the next state value.
9/15/09 - L21 Sequential Circuit Analaysis
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Generating Next State Use K maps generated from State Table
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The Circuit Using D FF
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Sequential Circuit analysis The circuit to
analyze
How to start? How about with
the next state equations?
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Next State Equations For DA have an AND-OR set of gates to
generate the input. The upper AND gate has inputs X and A The lower AND gate has inputs X and B So DA = AX + BX
For DB have a single AND gate whose inputs are X and A’ So DB = A’X
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Also have an output Y The OR gate has inputs A and B This feeds into a 2-input AND gate whose
other input is X’ Thus Y = (A+B)X’
Now having these equations can construct the state table for the state machine
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The state table For generation of the next state you have the
Present State as indicated by A and B plus the input X. This next state becomes the current state on the clock.
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Another form of the state table Two-dimensional form of the same table
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The state diagram for this systems is
Not the notation on the diagram On transition arcs –
input/output
The state Diagram
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Class 21 assignment Covered sections 5-4 Problems for hand in
5-6 and 5-10 Problems for practice
5-7, 5-8, 5-9
Reading for next class: sections 5-5
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