Freescale Semiconductor TWR-MCF52259-Ethenet User Manual page 111

Packets are a block of information with a defined data structure. The packet is the lowest level of
the USB transfer hierarchy describing the physical layer of the interface. If you were to monitor
D+ and D- you would see the packet fields:
Packet Identifier
Address
Endpoint
Data
Frame number
CRC
Packets in More Detail
Token Packet format:
SOF Packet format:
Data Packet format:
Handshake Packet format:
CRC covers everything in the packet with the exception of the PID which
has its own error checking mechanism.
Field PID Address
Bits 8 7
Field PID Frame Number TM
Bits 8
Field PID
Bits 8
Field
Bits
Endpoint CRC
4 5
CRC
11 5
Data CRC
0-1023 16
PID
8