In digital logic, which statement correctly contrasts positive logic and negative logic?

In digital logic, which statement correctly contrasts positive logic and negative logic?

• A. Positive logic uses low (0) to indicate true; Negative logic uses high (1)
• B. Both use 1 as true, but positive uses 0 as false and negative uses 1 as false
• C. Positive logic uses 0 as true; Negative logic uses 1 as true
• D. Positive logic uses high (1) to indicate true; Negative logic uses low (0) to indicate true

Answer: (C)

Positive logic ties a true condition to a high voltage level, typically represented by 1. Negative logic flips that convention, so a true condition is indicated by a low voltage level, represented by 0. This means signals labeled as active or true are high in positive logic and low in negative logic, respectively. In practice, many systems use negative logic for active-low signals because they can be wired so that the default state is a safe, high level and an active event pulls the line down to 0; for example, an active-low reset is held high by a resistor and pulls to 0 to reset. So the correct contrast is that positive logic uses high (1) for true, while negative logic uses low (0) for true.

Positive logic ties a true condition to a high voltage level, typically represented by 1. Negative logic flips that convention, so a true condition is indicated by a low voltage level, represented by 0. This means signals labeled as active or true are high in positive logic and low in negative logic, respectively. In practice, many systems use negative logic for active-low signals because they can be wired so that the default state is a safe, high level and an active event pulls the line down to 0; for example, an active-low reset is held high by a resistor and pulls to 0 to reset. So the correct contrast is that positive logic uses high (1) for true, while negative logic uses low (0) for true.