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Design mealy sequence detector to detect a sequence (1101-output signal)(Non-Overlapping sequence recognizer)

Please explain how to get the diagram

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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 Mealy Sequence Detector for the sequence 1101 in detail.

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

Mealy 1101 NO

  • Required less number of states as compared with Moore.

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

Mealy 1101 St

  • Output in a Mealy sequential circuit is associated with a current state and external inputs X.

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

Mealy 1101 et

  • Output depends on the current input and current state of the circuit.

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

Block Diagram Mealy Machine

  • Mealy circuit is associated with a transition between states.
  • Asynchronous output generation though the state changes synchronously to the clock.
  • Faster, the output is generated on the same clock cycle.
  • Glitches can be generated as output change depends on input transition.
  • Unsynchronized input may result in an invalid output is a major drawback of mealy.
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