Freescale Semiconductor TWR-MCF52259-Ethenet manual General USB Process

Software – General Concepts

The General USB Process

How Data is Transferred in USB

USB is a token-based (packet) standard. Data is transferred between the host and the device in a series of frames, transfers, transactions, and packets within1 Ms/1500 byte frames.

Frame

TM

Transfer 1

Transfer 2

Transfer 3

Transaction

Transaction 1

Transaction 2

Transaction 3

Transaction 1

Start of Frame

Packet 1

Packet 2

Packet 3

Packet 1

Packet 2

Packet 3

Packet 1

Packet 2

Packet 3

Packet 1

Packet 2

Packet 3

1500 bytes / 1 Ms