PLA

Introduction

• PLA stands for Programmable Logic Array.

Definition

• A Programmable Logic Array (PLA) is a digital logic device that allows us to implement/create a customized type of combinational logic circuits as needed.

Characteristic Features

• The advantages of PLAs include flexibility and the ability to implement custom logic functions without the need for custom IC design. However, PLAs can be relatively complex and may have limitations in terms of speed and power consumption for very high-speed applications.

Structure & Working Principle

• A Program Logic Array (PLA) is a digital circuit that consists of both programmable AND gates and programmable OR gates but a  typical PLA consists of three main components:-

1. 1. Input Buffer:
      • This component provides input signal conditioning.
      • It takes the input signals and prepares them for processing within the PLA.
   2. AND Array (AND Plane):
      • The AND array consists of a grid of programmable AND gates.
      • Each AND gate can take multiple inputs from the input buffer or external inputs. The connections between input signals and AND gates can be programmed to create specific logic functions. The outputs of these AND gates feed into the OR array.
   3. OR Array (OR Plane):
      • The OR array consists of programmable OR gates.
      • These gates take inputs from the AND array’s outputs and can also accept external inputs.
      • The OR gates generate the final outputs of the PLA.

• The programming of a PLA involves configuring the connections between the input signals, the AND gates in the AND array, and the OR gates in the OR array.
• This programming process is typically done using a hardware description language (HDL) or a dedicated hardware description tool.
• The goal is to define the desired logic function by specifying how inputs should be combined using AND gates and how their outputs should be combined using OR gates.

Use/Applications

• PLAs are often used in applications where custom logic functions are required, such as in microcontrollers, digital signal processors, and other complex digital systems.
• PLAs are often used in various digital applications, including control logic, arithmetic units, and data path control in microprocessors and other digital systems.
• PLA provides a way to implement custom logic circuits efficiently while maintaining flexibility for future design changes.
• It is a type of programmable logic device (PLD) used in digital circuit design.
• PLAs are used to create circuits for functions that require complex Boolean logic operations, and they can be programmed or configured to implement specific logic functions.