Logic Gates Using Inverters
1. Download the "Gates Using Inverters" Simulation and run it by pressing this button:
2. The simulation will have seven panels of different gates. The main gate of each panel is large and in red. The inputs and outputs to each main gate can be optionally be connected to NOT gates by switches. These NOT gates are smaller and in white.
In the diagram of the NOT gate panel below you can see that the first switch on the left hand side is the main input switch to the main gate of the panel. The indicator to the right of the main input switch displays weather a 0 or 1 has been selected. The next switch is for choosing between the upper path directly to the input of the gate or the lower path with a NOT gate inverter before the input of the gate. The green lights show the direction of the current flow. There is another indicator to confirm what value is actually going in to the main gate.
From the output of the main gate, there is another switch for choosing between the upper path directly from the output of the gate or the lower path with a NOT gate inverter after the output of the main gate. The final indicator shows the final output from the logic circuit.
3. Use the NOT gate panel to see how the NOT gates will keep inverting the values.
4. The rest of the panels work in the same way as the NOT panel but with two inputs both with optional inverters.
5. You can convert the AND gate in to a NAND gate by switching the output down the NOT gate path. A NAND gate is the same as an AND gate with an inverted output. The NAND gate functions can now be observed by operating the two main input switches.
6. Now switch the output switch back up so that the output goes through the clear upper path. Now switch the two input switches down, so that they use the lower paths with the NOT gate inverters. The inputs to the main gate are now inverted. Try operating the input switches and you should see that a NOR gate has been made out of the AND gate by inverting the inputs.
7. If yo now keep the current circuit configuration and switch the output down the NOT gate path, you will have virtually inverted the output from the created NOR gate making an OR gate.
So by using inverters with an AND gate, you can produce a NAND, NOR and OR logic gate.
8. Repeat the experiment with the rest of the panels in the simulation and see what gates can be produced from each one. When you have completed the experiment, you can check the answers.
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Richard Bigwood 2005