Lecture Notes: Sequential Logic, Finite State Machines, and HDL

Introduction

• Continuation of the previous week's topics: Sequential logic and finite state machines (FSMs).
• Today's focus: Completing sequential logic design and introduction to Hardware Description Language (HDL) and Verilog.
• Recap of covered material with focus on green topics; blue topics to be covered today.

Sequential Circuits

• Definition: Produce outputs determined by current inputs and past values; circuits with memory.
• Comparison with Combinational Circuits: Sequential circuits include elements like state machines; combinational circuits do not have memory.
• State Machine Design: Pictorial representation of discrete time model; involves finite states, inputs, outputs, and state transitions.

Finite State Machines (FSMs)

• Components:
  • State Register: Stores the current state.
  • Next State Logic: Determines the next state from the current state and inputs.
  • Output Logic: Determines outputs based on current state.
• Example: Traffic light controller FSM with more and Mealy types.

FSM Design Process

1. Determine States and Transitions:
   • Define possible states and transitions based on inputs and current state.
   • Use pictorial state diagrams for visualization.
2. State Transition Table:
   • Convert pictorial representation to a truth table.
   • Encode states using binary or one-hot encoding.
3. Next State and Output Logic:
   • Express next state and output logic in Boolean expressions.
   • Simplify using sum of products or Karnaugh maps.

State Encoding

• Methods:
  • Binary Encoding: Minimizes flip-flops but may increase logic complexity.
  • One-Hot Encoding: Each bit represents a state; simplifies logic but uses more flip-flops.
  • Output Encoding: States encode output directly; useful for Moore machines.

Timing in FSMs

• Clock Cycle: Must accommodate longest combinational logic delay for proper operation.
• Timing Diagrams: Visualize state transitions and timing requirements.
• Importance: Ensures correct state transitions and outputs.

FSM Types

• Moore Machine: Output depends only on the current state.
• Mealy Machine: Output depends on current state and inputs, allowing fewer states but more complex output logic.

Practical Applications and Labs

• Overview of lab exercises emphasizing FPGA usage.
• Field Programmable Gate Arrays (FPGA):
  • Reconfigurable hardware substrate for designing digital circuits.
  • Use in various applications like deep learning, bioinformatics, and hardware prototyping.

Verilog and HDL

• Purpose: Describe digital circuits at various abstraction levels.
• Key Features:
  • Hierarchical design: Modules and submodules.
  • Supports concurrency in hardware design.
• Example: Simple module definition with inputs and outputs.

Conclusion

• Preparation for designing a microprocessor in labs using foundational knowledge of FSMs and HDL.
• Importance of understanding the underlying hardware implementation for effective design and optimization.