In USB serial communication, which statement defines a logical one?

In USB serial communication, which statement defines a logical one?

• A. A 1 is defined as D+ 200 mV greater than D-.
• B. A 1 is defined as D+ 200 mV less than D-.
• C. A 0 is defined as D+ 200 mV greater than D-.
• D. A 0 is defined as D+ 200 mV less than D-.

Answer: (A)

USB uses the D+ and D- lines as a differential pair, so the data is read from the polarity of the voltage difference between them rather than absolute levels. A logical one is represented when D+ is higher than D- by about 200 mV. The receiver looks at the sign of V(D+) − V(D−); a positive difference around 0.2 V is interpreted as a 1, while a negative difference of similar magnitude would be a 0. This arrangement provides noise tolerance because only the difference in voltage matters. So the statement that defines a logical one is that D+ is about 200 mV greater than D−.

USB uses the D+ and D- lines as a differential pair, so the data is read from the polarity of the voltage difference between them rather than absolute levels. A logical one is represented when D+ is higher than D- by about 200 mV. The receiver looks at the sign of V(D+) − V(D−); a positive difference around 0.2 V is interpreted as a 1, while a negative difference of similar magnitude would be a 0. This arrangement provides noise tolerance because only the difference in voltage matters. So the statement that defines a logical one is that D+ is about 200 mV greater than D−.