Freescale Semiconductor TWR-MCF52259-Ethenet - Manual (Page 95)

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The General USB Process
How Data is Transferred in USB
For each transaction there are three types of packets that
communicate the data between host and device:
Transaction Transaction
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P
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1. Token Packet – the header that defines what follows
2. Optional Data Packet – contains the data being transmitted
3. Status/Handshake Packet – used to acknowledge transactions
and provide a means of error correction