Este capítulo describe la especificación eléctrica para el USB. It contains signaling, power distribution, and physical layer specifications. This specification does not address regulatory compliance. It is the responsibility of product designers to make sure that their designs comply with all applicable regulatory requirements.

The USB 2.0 specification requires hubs to support high-speed mode. USB 2.0 devices are not required to support high-speed mode. A high-speed capable upstream facing transceiver must not support low-speed signaling mode. A USB 2.0 downstream facing transceiver must support high-speed, full-speed, and low-speed modes.

To assure reliable operation at high-speed data rates, this specification requires the use of cables that conform to all current cable specifications.

In this chapter, there are numerous references to strings of J’s and K’s, or to strings of 1’s and 0’s. In each of these instances, the leftmost symbol is transmitted/received first, and the rightmost is transmitted/received last.