Specification
NET2272 USB Peripheral Controller
______________________________________________________________________________
NetChip Technology, Inc., 2003
Patent Pending
335 Pioneer Way, Mountain View, California 94041
TEL (650) 526-1490
FAX (650) 526-1494
http://www.netchip.com
Rev 1.2, October 15, 2003
32
5
USB Functional Description
5.1
USB Interface
The NET2272 is a USB function device, and as a result is always a slave to the USB host. The bit and packet level
protocols, as well as the electrical interface of the NET2272, conform to USB Specification Version 2.0. The USB
host initiates all USB data transfers to and from the NET2272 USB port. The NET2272 can be configured for up to
3 physical and 30 virtual endpoints, in addition to Endpoint 0. Each endpoint can be an isochronous, bulk or
interrupt type. The configuration registers are used to program the characteristics of each endpoint. The NET2272
operates in either Full speed (12 Mbps) or High speed (480 Mbps) modes.
5.2
USB Protocol
The packet protocol of the USB bus consists of tokens, packets, transactions, and transfers.
5.2.1 Tokens
Tokens are a type of Packet Identifier (PID), and follow the sync byte at the beginning of a token packet. The four
classic types of tokens are OUT, IN, SOF, and SETUP. In high speed mode, the NET2272 also recognizes the
PING token.
5.2.2 Packets
There are four types of packets: start-of-frame (SOF), token, data, and handshake. Each packet begins with a sync
field and a Packet Identifier (PID). The other fields vary depending on the type of packet.
An SOF packet consists of the following fields:
•
Sync byte (8-bits)
•
Packet Identifier (8-bits)
•
Frame Number (11-bits)
•
CRC (5-bits)
A token packet consists of the following fields:
•
Sync byte (8-bits)
•
Packet Identifier (8-bits)
•
Address (7-bits)
•
Endpoint (4-bits)
•
CRC (5-bits)
A data packet consists of the following fields: a token packet always precedes Data packets.
•
Sync byte (8-bits)
•
Packet Identifier (8-bits)
•
Data (n bytes)
•
CRC (16-bits)
A handshake packet consists of the following fields:
•
Sync byte (8-bits)
•
Packet Identifier (8-bits)
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