Technical Reference Guide
5.7.1 USB DATA FORMATS
The USB I/F uses
♦Sync Field –
♦Packet Identifier (PID) Field –
♦Address Field –
♦Endpoint Field –
♦Frame Field –
♦Data Field –
♦Cyclic Redundancy Check (CRC) Field – 5- or
Token Packet
SOF Packet
Data Packet
Handshake Packet
Sync Field | PID Field | Addr. Field |
| ENDP. Field |
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| CRC Field |
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(8 bits) | (8 bits) | (7 bits) |
| (4 bits) |
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| (5 bits) |
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Sync Field | PID Field | Frame Field |
| CRC | Field |
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(8 bits) | (8 bits) | (11 bits) |
| (5 bits) |
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Sync Field | PID Field | Data Field |
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(8 bits) | (8 bits) |
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Sync Field | PID Field |
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(8 bits) | (8 bits) |
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Figure 5-8. USB Packet Formats
Data is transferred LSb first. A cyclic redundancy check (CRC) is applied to all packets (except a handshake packet). A packet causing a CRC error is generally completely ignored by the receiver.
Compaq D315 and hp d325 Personal
Featuring the AMD Athlon XP Processor
Second Edition - April 2003