Basics of Programmable Logic - History of Digital Logic Design

Introduction

• Presenter: Carl
• Overview of the training: Exploration of programmable logic devices (PLDs) leading up to modern FPGAs.
• Importance: Programmable logic is ubiquitous (e.g., HDTVs, cell towers, ATMs).
• Goals: Understand technology, history, functionality, and desirability of programmable logic for designers.

History of Logic Design

Early Digital Logic Design

• Designers used multiple chips wired together on circuit boards.
• Chips included basic logic gates (NAND, AND, OR) and structures (flip-flops, multiplexers).
• Popular series: Texas Instrument 7400 series (TTL - Transistor-Transistor Logic).
• Goals: Minimize cost, board space, and number of chips.
• Optimization challenges: Design adjustments required to maintain functionality.

Logic Design Process

1. Truth Table Creation
   • Lists all possible inputs and associated outputs.
2. Karnaugh Map (K-map)
   • Organizes outputs into a grid based on inputs.
   • Minterms: Combinations producing an output of 1.
3. Simplification
   • Draw boxes around minterms to create simplified logic expressions.
   • Result: Sum of Products to implement in hardware (AND gates, OR gates).

Programmable Logic Devices (PLD)

Transition from Traditional Logic to PALs

• Concept: Combine gates and registers in a single device.
• Programmable Array Logic (PAL)
  • Fixed logic gates, programmable connections.
  • Structure:
    • Programmable array: Selects inputs to route to AND gates.
    • OR gate: Generates final function output, fed through a register.

Advantages of PALs

• Fewer devices needed = lower cost, reduced board space, easier debugging.
• Provides design security and flexibility.
• Supports in-system programmability and reprogrammability.

Programming Methods

• Floating Gate Transistors: Used for programming PALs/PLDs.
  • Types: Floating gate avalanche injection MOS and FLOTOX.
  • Programming involves trapping electrons on the floating gate.

Complex Programmable Logic Devices (CPLD)

• Built from multiple PLD blocks interconnected.
• 22V10: First PLD with fully programmable macrocells and variable product term distribution.
• CPLD advantages:
  • More logic and routing options.
  • Enhanced I/O features and capabilities.
  • Instant-on operation and low power consumption.

Modern FPGA Devices

• Architecture improvements over CPLDs.
• Building blocks: Logic elements or adaptive logic modules, memory blocks, DSP blocks, PLLs, transceivers.
• Further exploration in follow-on training on FPGA architecture.

References

• Intel FPGA Training webpage for more on FPGA capabilities.
• Altera's Technical Documentation for comprehensive information.
• Article: "The History of Programmable Logic Technology" in Altera's System Design Journal.

Conclusion

• Feedback survey for training material improvement.
• Good luck with designs!