Diode logic uses diodes as electrical switches to create Boolean “AND” and “OR” logic gates in circuits. Boolean logic is similar to search engine logic, with high and low voltages representing “true” and “false” outputs. Diode logic gates can only be used for simple functions and cannot be linked together without errors.
Diode logic uses diodes to create Boolean logic gates in electrical circuits. Diodes act as electrical switches in these circuits because they can only conduct current in one direction. Diode logic can only be used to construct Boolean “AND” and “OR” logic functions due to the simple nature of diodes.
Boolean logic in computer circuitry and programming is similar to the more common Boolean logic used by search engines. If a searcher types ham AND eggs into a search engine, the results will contain both words. On the other hand, if the searcher types ham OR eggs, the search engine returns results that contain both words or just one of the words. This means that the AND function narrows the results, but the OR function broadens them.
In electrical circuits, voltages replace search terms and results used in a search engine. The only possible results are a high voltage or a low voltage, represented by the numbers 1 and 0 respectively. An output of 1 represents a positive result or a “true” output. The 0 represents a negative result, which returns “false”.
For an AND diode logic circuit, both inputs must have high voltages—that is, they must be “true”—for the output to be true as well. A diode has a logic value of 1 if it is connected to a power source and therefore voltage flows through it, and a logic value of 0 if it is disconnected. When either or both diodes in the AND circuit are disconnected, the voltage cannot reach the output lead and will have a logical value of 0. Only one of four possible scenarios: 0 and 0, 1 and 0, 0 and 1, or 1 and 1 – results in a voltage reaching the diode for an output of 1.
In an OR diode logic circuit, on the other hand, three of the four possible scenarios result in a real output. Only the input of 0 and 0 returns false output. This happens because the diodes are connected in such a way that the output wire receives voltage when one or both diodes are connected.
Diode logic gates are useful for simple AND and OR functions, but cannot be used to link multiple AND and OR functions together. This is because two logic gates connected to another logic gate lead to incorrect voltage readings at the output for the third gate. The effect becomes even worse if more gates are connected. Diode logic gates are only used one at a time to avoid these errors.
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