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Sequentional Circuit Analysis

1) The document outlines the steps in designing a sequential circuit, including specification, state diagram/table generation, state assignment, flip-flop input/output equation generation, optimization, and verification. 2) It also discusses the differences between Mealy and Moore machines, with Moore machines having outputs dependent only on current state and Mealy machines having outputs dependent on both current state and inputs. 3) An example design is provided for a circuit with one input and one output, where the output is 1 only when the input sequence 1101 is detected, going through the design steps.

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Mohan Awasthy
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54 views5 pages

Sequentional Circuit Analysis

1) The document outlines the steps in designing a sequential circuit, including specification, state diagram/table generation, state assignment, flip-flop input/output equation generation, optimization, and verification. 2) It also discusses the differences between Mealy and Moore machines, with Moore machines having outputs dependent only on current state and Mealy machines having outputs dependent on both current state and inputs. 3) An example design is provided for a circuit with one input and one output, where the output is 1 only when the input sequence 1101 is detected, going through the design steps.

Uploaded by

Mohan Awasthy
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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S equential circuit design and analysis

 Steps in the design process for sequential circuits


 State Diagrams and State Tables
 Examples

 Steps in Design of a Sequential Circuit


1. Specification – A description of the sequential circuit. Should include a detailing of the inputs,
the outputs, and the operation. Possibly assumes that you have knowledge of digital system basics.
2. Formulation: Generate a state diagram and/or a state table from the statement of the problem.
3. State Assignment: From a state table assign binary codes to the states.
4. Flip-flop Input Equation Generation: Select the type of flip-flop for the circuit and generate
the needed input for the required state transitions
5. Output Equation Generation: Derive output logic equations for generation of the output from
the inputs and current state.
6. Optimization: Optimize the input and output equations. Today, CAD systems are typically
used for this in real systems.
7. Technology Mapping: Generate a logic diagram of the circuit using ANDs, ORs, Inverters,
and F/Fs.
8. Verification: Use a HDL to verify the design.
Mealy and Moore
 Sequential machines are typically classified as either a Mealy machine or a Moore
machine implementation.
 Moore machine: The outputs of the circuit depend only upon the current state of the
circuit.
 Mealy machine: The outputs of the circuit depend upon both the current state of the
circuit and the inputs.

An example to go through the steps


The specification: The circuit will have one input, X, and one output, Z. The output Z will be 0
except when the input sequence 1101 are the last 4 inputs received on X. In that case it will be a
1
Generation of a state diagram
 Create states and meaning for them.
State A – the last input was a 0 and previous inputs unknown. Can also be the reset state.
State B – the last input was a 1 and the previous input was a 0. The start of a new sequence
possibly.
 Capture this in a state diagram
Capture this in a state diagram

Circles represent the states


Lines and arcs represent the transition between states.
The notation Input/output on the line or arc specifies the input that causes this transition
and the output for this change of state.
 Add a state C – Have detected the input sequence 11 which is the start of the sequence

Add a state D
State D – have detected the 3rd input in the start of a sequence, a 0, now having
110. From State D, if the next input is a 1 the sequence has been detected and a 1
is output.

The previous diagram was incomplete.


In each state the next input could be a 0 or a 1. This must be included
 The state table

 This can be done directly from the state diagram

 Now need to do a state assignment

Select a state assignment

 Will select a gray encoding


 For this state A will be encoded 00, state B 01, state C 11 and state D 10

Flip-flop input equations

 Generate the equations for the flip-flop inputs


 Generate the D0 equation

 Generate the D1 equation


The output equation
 The next step is to generate the equation for the output Z and what is needed to generate
it.
 Create a K-map from the truth table.

Now map to a circuit

 The circuit has 2 D type F/Fs

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