design 101 sequence detector using non-overlapping mealy machine with d flip-flop.

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Design a Non-Overlapping Moore Sequence Detector for the sequence 1101

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written 11 months ago by

binitamayekar ★ 5.8k

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Sequence Detector

A Sequence detector is a sequential state machine used to detect consecutive bits in a binary string.

To do this it takes an input string of bits and generates an output of 1 whenever the target sequence has been detected.

Finite State Machine (FSM), an important category of sequential circuits, is used frequently in designing digital systems.

There are two main FSM models for sequential circuits:

Mealy Model - In this type of circuit the output depends on the external inputs and the current state of the machine.Moore Model - In this type of circuit the output of the system only depends on the current state of the machine.

There are two types of sequence detectors depending on the type of sequence they identify, which are as follows:

Overlapping Sequence Detector:

In this type of sequence detector allows overlap, the final bits of one sequence can be the start of another sequence.

For example, will be an 1101 sequence detector. It raises an output of 1 when the last 4 binary bits received are 1101.Non-Overlapping Sequence Detector:

In this type of sequence detector does not allow overlap, but resets itself to the start state when the sequence has been detected.

For example, after the initial sequence 1101 has been detected, the detector with no overlap resets and starts searching for the initial 1 of the next sequence.

Here, we see Non-Overlapping Moore Sequence Detector for the sequence 1101 in detail.

State diagram for 1101 sequence detector using Moore machine (Non - Overlapping):

A Moore state diagram produces a unique output for every state irrespective of inputs.

State table for 1101 sequence detector using Moore machine (Non - Overlapping):

Output in a Moore sequential circuit is associated with a current state only.

The output Y does not depend on input X.

Excitation table for 1101 sequence detector using Moore machine (Non - Overlapping):

This Excitation Table indicates that Combinational logic is divided into two parts

Next state logic depends on input and current state.

Output logic depends on the current state only.

Block diagram for 1101 sequence detector using Moore machine (Non - Overlapping):

Both output and state change synchronous to the clock edge.

The output is generally produced in the next clock cycle.

Safer to use because states change on the clock edge.

Output depends only on the present state of the circuit only.

It uses more states than the Mealy machine. Therefore, circuit implementation needs more cost.

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Design 101 sequence detector (Mealy machine)

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Design 101 sequence detector (Mealy machine)

Difficulty Level : Medium

Last Updated : 01 Apr, 2021

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Prerequisite – Mealy and Moore machines

A sequence detector is a sequential state machine that takes an input string of bits and generates an output 1 whenever the target sequence has been detected. In a Mealy machine, output depends on the present state and the external input (x). Hence, in the diagram, the output is written outside the states, along with inputs. Sequence detector is of two types:

Overlapping Non-Overlapping

In an overlapping sequence detector, the last bit of one sequence becomes the first bit of the next sequence. However, in a non-overlapping sequence detector, the last bit of one sequence does not become the first bit of the next sequence. In this post, we’ll discuss the design procedure for non-overlapping 101 Mealy sequence detectors.

Examples:

For non overlapping case

Input :0110101011001

Output:0000100010000

For overlapping case

Input :0110101011001

Output:0000101010000

The steps to design a non-overlapping 101 Mealy sequence detectors are:

Step 1: Develop the state diagram –

The state diagram of a Mealy machine for a 101 sequence detector is:

Step 2: Code Assignment –Rule 1 : States having the same next states for a given input condition should have adjacent assignments.Rule 2: States that are the next states to a single state must be given adjacent assignments.

Rule 1 given preference over Rule 2.