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Document provides a detailed overview of encoders and decoders, their functions, types, and applications in digital circuits.

Introduction

  • Encoders and decoders are essential components in digital electronics.
  • They are used to convert data from one format to another.

Decoders

  • Definition: A decoder is a logic circuit that converts binary input into a specific output.
  • Function: Activates only the output corresponding to the binary input number.
  • General Form: Has ( N ) input lines and ( 2^N ) output lines.
  • Basic Binary Function: AND gates are used as the basic decoding elements.
  • Types:
    • Active-LOW Output: Implemented with NAND gates and inverters.
    • Active-HIGH Output: Implemented with AND gates and inverters.
  • Examples:
    • 2-to-4 Line Decoder: Operates with complemented outputs and a complement enable input.
    • 3-to-8 Line Decoder: Also known as a binary-octal decoder, activates one of eight outputs based on a three-bit input code.
  • Applications: Used in computers for I/O selection, enabling communication with peripherals through input/output ports.

Encoders

  • Definition: An encoder is a combinational logic circuit that performs the reverse function of a decoder.
  • Function: Converts an active input into a coded output.
  • General Form: Has multiple input lines and produces an ( N )-bit output code.
  • Types:
    • Octal-to-Binary Encoder: Converts octal inputs to binary outputs.
    • Priority Encoder: Includes a priority function to handle multiple active inputs by prioritizing the highest-order input.
  • Examples:
    • 4-Input Priority Encoder: Produces a binary output corresponding to the highest-priority active input.
    • Decimal-BCD Priority Encoder: Converts decimal inputs to BCD outputs, prioritizing the highest-order input.
    • Octal-to-Binary Priority Encoder: Converts octal inputs to binary outputs with priority encoding.
    • 16-to-4 Encoder: Expanded from an 8-to-3 encoder by connecting outputs and inputs appropriately.

Application Example

  • Keyboard Encoder: Simplified example of an encoder used in keyboards to convert key presses into binary codes.

Encoders and Decoders – Lesson 11

Engineering Institute of Technology