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Introduction to Programmable Logic Devices. Aleksandra Kovacevic [email protected] Veljko Milutinovic [email protected] 0/13. Introduction Comparison of Standard Logic Circuits and Programmable Logic Circuits Evolution and Overview of PLC: PROM, PLA, PAL CPLD FPGA. 1/13.

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Introduction to Programmable Logic Devices

Aleksandra Kovacevic

[email protected]ro.yu

Veljko Milutinovic

[email protected]


  • Introduction

  • Comparison of Standard Logic Circuits and Programmable Logic Circuits

  • Evolution and Overview of PLC:

    • PROM, PLA, PAL

    • CPLD

    • FPGA


  • Standard Logic Circuits

  • Appropriate for many applications because of possibility of realization in mass production for relative low cost.

  • Standard logic circuits are sometimes the best choice in high-performance devices.

  • Disadvantage:Not permitting design updates (function changes) with no hardware replacement necessary.


  • Field- Programmable Logic Devices

  • Component function is defined by users program.

  • Logic Cells Fields are interconnected by programming.

  • Advantages:

    • Flexible design that changes by reprogramming, ease of design changes

    • Reduce prototype-product time

    • Large scale integration (over 100 000 gates)

    • Reliability increased, low financial risk

    • Smaller device, low start-up cost


  • FPLDs Representatives

  • PLA - Programmable Logic Arrays

  • PAL - Programmable Array Logic

  • CPLD - Complex Programmable Logic Devices

  • FPGA - Field Programmable Gate Arrays

Programmable logic device



Evolution of PLD: Why not PROM?

  • A special device (called a burner), used to put the information, supplies an electrical current to specific cells in the ROM that effectively blows a fuse in them = burning the PROM. From that point on, chip is read-only.

  • PROM was the first type of user-programmable chip; address lines = logic circuit inputs data lines = logic circuit outputs

  • PROMs are inefficient architecture for realizing logic circuit:

Logic functions rarely require more than few product terms

PROM contains a full decoder for its address inputs.


Evolution of PLD: PLA

  • PLA was the first device developed for implementing

  • Consist of two levels of logic gates - programmable “wired” AND-plane & OR-plane

  • Drawbacks:

    • Expensive to manufacture

    • Offered somewhat poor speed-performance



Evolution of PLD: PAL™

  • Overcame weaknesses of PLA

  • Single level of programmability - consists of a programmable “wired” AND-plane & fixed OR-gates

  • Simpler to program and cheaper implementation

  • Limited numbers of terms in each output



PALis a trademark of Advanced Micro Devices

sequential circuits can be realized

Evolution of PLD: RegisterPLA

  • Contain flip flops connected to the OR gate outputs

  • Importance:

    • Profound effect ondigital hardware design

    • Basis for more sophisticated architectures


Evolution of PLD: CPLD

Programmable Interconnect Array

- Capable of connecting any LAB input or output to any other LAB

possibility to produce devices with higher capacity than SPLDs.

  • Technology advanced

  • Structure grows too quickly in size as the number of inputs is increased

  • Integrating multiple SPLDs onto a single chip - the only feasible way to provide large capacity devices based on SPLD

    • Programmably connect the SPLD blocks together

    • Logic capacity up to the equivalent of about 50 typical SPLD devices

Logic Array Blocks

- Complex SPLD-like structure


Evolution of PLD: FPGA

contains a set of basic functions (gates, FFs, memory cells)

  • Difficult extending CPLDs architectures to higher densities - adifferent approach is needed

  • FPGAs comprise an array of uncommited circuit elements, called logic blocks, and interconnect resources

  • FPGA configuration is performed through programming by the end user.

Xilinx FPGA Configuration


Introduction to Programmable Logic Devices

Aleksandra Kovacevic

[email protected]

Veljko Milutinovic

[email protected]