Advanced Projects in CEDAR Logic Simulator: From Flip-Flops to CPUs

Designing and Testing Circuits with CEDAR Logic Simulator: Step-by-Step Tutorial

Overview

A concise, practical walkthrough to design, simulate, and test digital circuits in CEDAR Logic Simulator. Assumes basic familiarity with logic gates and binary concepts.

1. Project setup

1. Open CEDAR and create a new project.
2. Set project name and workspace folder.
3. Choose target technology (TTL/CMOS) if available for timing models.

2. Create schematic

1. Place components: Use the component palette to add gates (AND, OR, NOT, XOR), inputs (switches/clock), outputs (LEDs/probes), and flip-flops.
2. Arrange neatly: Align and space components for readability.
3. Label signals: Add text labels for buses and key nets.

3. Wiring and buses

1. Connect pins: Draw wires between component pins; avoid crossing — use junction dots where needed.
2. Create buses: Group parallel signals into buses and use bus connectors for multi-bit buses.
3. Use net names: Assign net labels to connect distant parts without long wires.

4. Configure components

1. Set parameters: Double-click components to set widths (for buses), propagation delays, initial states for flip-flops, and pull-up/pull-downs.
2. Clock settings: Configure clock frequency, duty cycle, and phase for synchronous designs.

5. Simulation types

1. Logic (static) simulation: Verify combinational logic outputs for given inputs. Use manual switches to toggle inputs.
2. Timing simulation: Run with propagation delays to observe hazards, races, and setup/hold violations.
3. Event-driven vs. step simulation: Choose event-driven for large designs; step for pedagogical tracing.

6. Testbench and stimulus

1. Create test vectors: Use input sequence files or a pattern generator to apply systematic input combinations.
2. Automate clocks and resets: Include reset sequence at start and a stable clock for synchronous tests.
3. Self-checking tests: Add comparators to compare outputs to expected vectors and flag mismatches.

7. Observing outputs

1. Probes and LEDs: Attach probes to nets for live logic levels; use LEDs for simple visual checks.
2. Waveform viewer: Open the waveform panel to record and inspect signals over time; zoom and cursor for timing measurements.
3. Logging: Export signal traces or CSV for offline analysis.

8. Debugging techniques

1. Isolate blocks: Temporarily replace complex blocks with simpler models or fixed inputs.
2. Step through events: Run simulation step-by-step to trace transitions causing errors.
3. Check timing margins: Adjust delays or add synchronization registers to fix races and glitches.
4. Use assertions: If supported, add assertions to catch illegal states early.

9. Iteration and optimization

1. Refactor schematic: Simplify logic using Boolean identities or replace gate clusters with higher-level modules.
2. Optimize for area/speed: Trade off gate count vs. propagation delay by restructuring critical paths.
3. Parameter sweeps: Test different clock speeds and component delays to find safe operating margins.

10. Exporting and sharing

1. Save project files: Keep schematic, simulation settings, and testbenches together.
2. Export diagrams: Generate PNG/PDF of schematics for documentation.
3. Share waveforms: Export waveform files or CSV for collaborators.

Example quick walkthrough (4-bit ripple adder)

1. Place four 1-bit full adders in series.
2. Connect carry-out of each to carry-in of next; label carries.
3. Tie inputs to a bus and add switches or a vector file to apply test patterns.
4. Run timing simulation to observe worst-case carry propagation; view sum and carry waveforms.
5. Add probes on carry chain to measure propagation delay and identify bottlenecks.

Final tips

• Frequently save versions.
• Start testing small blocks before integrating.
• Use waveform comparisons for automated validation.

If you want, I can produce a printable one-page checklist or a 4-bit ripple-adder example file compatible with CEDAR.