POSITIVE AND NEGATIVE LOGIC DESIGNATION

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 Logical 1 and 0 are generally represented by voltage level. In a positive logic system, the most Positive voltage system (HIGH) represents the logical 1 status, and the most Negative voltage level (LOW) represents the logical 0 state. In a Negative logic system, the most Positive (HIGH) voltage level represents logical 0 state and the most Negative (LOW) voltage level represents logical 1 state. For example, if the voltage level are -0.1 and -5 V, then in a positive logic system the -5 V level represents a 0 state and the -0.1 level represents a 1 state; in a negative logic system, -0.1 level represents a 0 state and -5 V represents a 1 state. Conversely, if the voltage level are 0.1 V and 5 V, then in a positive logic system the 5 V level represents a 1 state and the 0.1 V represents a 0 state; in a negative logic system, the 0.1 V represents a 1 state and the 5 V level represents a 0 state.
           
          The effect of changing from one logic designation to the other is equivalent to complementing the logic function.The simple method of converting the logic designation is that all 0s are replaced with 1s and all 1s with 0s in the Truth Table. The resulting logic is determined accordingly. For example, when 0s and 1s are interchanged in the truth table, the positive logic AND gate becomes negative logic OR gate, and positive logic NAND gate becomes negative logic NOR gate. As there is no real advantage to either designation, the choice of positive or negative logic is logic is made by the individual logic designer.

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