Combinational Analysis in Logisim-evolution: From Truth Table to Circuit
Combinational Analysis lets you describe what a circuit should do — as a truth table — and generates the circuit for you. It is the fastest way to go from a specification to working logic, and a great way to check hand-drawn designs.
Step 1: Open Combinational Analysis
Choose Project → Analyze Circuit. The window normally analyzes the current circuit, but you can also use it as a blank designer: define your own inputs, outputs, and table from scratch.
Step 2: Define inputs and outputs
Click the Inputs & Outputs tab. Use the Add buttons to create input variables (for example a and b) and output variables (for example out). Keep the numbers small — the table doubles in size with each added input, so the tool works best with a handful of inputs.
Step 3: Fill in the truth table
Switch to the Table tab and click output cells to set each row’s result. As an example, build a 2-input XOR: set the output to 1 only in the rows (0, 1) and (1, 0).
Step 4: Check the minimized expression
Open the Minimized tab and click Optimize minterms (or Optimize maxterms for product-of-sums). Logisim-evolution shows the simplified Boolean expression — compare it against your own Karnaugh-map solution.
Step 5: Build the circuit
Click Build Circuit. Logisim-evolution generates a circuit implementing your table and asks whether to replace the current circuit or create a new one. Pick a new circuit to keep your original work, then open it and test it with the Poke tool.
When to use it
- Checking homework: design by hand first, then compare against the generated circuit.
- Starting a design: prototype the logic quickly, then refine the generated circuit.
- Learning minimization: the Minimized tab shows what the optimal expression looks like.