Learn USB Protocol

5.Define USB

  • Serial protocol—strictly defined frame and packet based protocol with error checking and handshaking. LSB in first, MSB last.
  • Half Duplex—all transactions initiated by the host with data carried by the D+ and D- signals in both directions.
  • Device Management—host assigns addresses to newly attached devices and removes support for detached devices. Host also manages bandwidth.
  • Power Management—use of Suspend mode to conserve power on the bus. Vbus sourced by host is +5V ±5%.
  • Direction—all transactions are directed with respect to the host. IN transactions send data from the peripheral to the host. OUT transactions send data from the host to the peripheral.


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