3-Input OR Gate

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Description

This MicroSim provides an interactive demonstration of a 3-input OR gate. The simulation displays the standard OR gate symbol with its curved body, three clickable input toggles, and a complete eight-row truth table.

The 3-input OR gate outputs 1 when any one or more of the three inputs is 1. The output is 0 only when all three inputs are 0. As you toggle inputs, the truth table highlights the current row in real time.

Key Features

  • ● Standard OR gate symbol with three input wires and one output wire
  • ● Three clickable toggle buttons for inputs A, B, and C
  • ● Eight-row truth table with real-time row highlighting
  • ● Live output display showing the Boolean expression A OR B OR C = Y

How to Use

  1. Click the toggle button next to input A to switch it between 0 and 1
  2. Click the toggle button next to input B to switch it between 0 and 1
  3. Click the toggle button next to input C to switch it between 0 and 1
  4. Observe the gate output update in real time
  5. Watch the truth table highlight the row matching the current input combination
  6. Verify that the output is 0 only when all three inputs are 0

Learning Objectives

Bloom Level: Understand (L2)

After using this MicroSim, students will be able to:

  • ✓ Extend the 2-input OR gate concept to three or more inputs
  • ✓ Predict the output of a 3-input OR gate for any input combination
  • ✓ Explain why the OR gate outputs 0 for only one of the eight possible input combinations
  • ✓ Relate the 3-input OR gate to its Boolean expression Y = A + B + C

Lesson Plan

Before the Simulation (5 minutes)

  • ● Review the 2-input OR gate and its truth table
  • ● Ask students how many rows produce output 1 for a 3-input OR gate
  • ● Introduce the idea that OR generalizes to any number of inputs

During the Simulation (15 minutes)

  1. Start with all inputs at 0 and verify the output is 0
  2. Toggle input A to 1 and observe the output becomes 1
  3. Toggle additional inputs and observe the output remains 1
  4. Find the single combination that produces output 0 (A=0, B=0, C=0)
  5. Count how many of the 8 rows produce output 1 versus output 0 (seven vs. one)
  6. Compare this pattern with the AND gate (which has the opposite ratio)

After the Simulation (5 minutes)

  • ● Discuss how OR gates are used in interrupt priority logic
  • ● Ask students to predict the truth table for a 4-input OR gate
  • ● Connect to the NOR gate as the complement of OR

References