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Logisim–Microprocessor and Computer Architecture

  • Best tool for designing and simulating circuits on virtual breadboard.
  • Some other alternative tools are “Digital”,
  • This tool is built-on Java environment. So your system needs Java installation.
  • During Logisim installation, it automatically pops for java installation , if you have internet working on your machine.
  • Link to download Logisim is :
  • This help option provides the tutorial to understand basics.
  • Let’s understand how to create a circuit:
    • Question is: Implement the following logic function using basic gates and test the output using truth table.
    • Y = ABC + DE + F
  • To solve this question we need two AND gates, because ‘ABC’ and ‘DE’ are in multiplication(i.e AND gate is required to calculate their bitwise multiplication) and ‘ABC’, ‘DE’, ‘F’ are getting added, so we need a three input OR gate to calculate final answer.
  • To change five input AND gate to as per question requirement, we change Number of inputs from the selection pane and select “3 “for first AND gate and “2” for second AND gate.
  • Similarly, we select 3 inputs for OR gate, because we are adding three terms in the question.
  • The final circuit is:
  • For simulation of circuit we click on input square and look for change in output. In the above figure all inputs are zero hence output is zero, as per the calculation.
  • As we toggle the input using hand, the value of output gets change as well as the color coding of input, which is playing major role in producing the output as ‘1’ as seen in above figure.
  • To analyse the circuit and create a truth table we use the option project->Analyse Circuit
  • The project is saved using File->save. The project will be saved with .circ extention.

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