User manual

TM
Software – General Concepts
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Packets in More Detail
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
5478Bits
CRCEndpointAddressPIDField
Token Packet format:
5118Bits
CRCFrame NumberPIDField
SOF Packet format:
160-10238Bits
CRCDataPIDField
Data Packet format:
8Bits
PIDField
Handshake Packet format:
CRC covers everything in the packet with the exception of the PID which
has its own error checking mechanism.