Specification
NET2270 USB Interface Controller
______________________________________________________________________________
NetChip Technology, Inc., 2003
335 Pioneer Way, Mountain View, California 94041
TEL (650) 526-1490
FAX (650) 526-1494
http://www.netchip.com
Rev 3.6, April 17, 2003
29
5
USB Functional Description
5.1
USB Interface
The NET2270 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 NET2270, conform to USB Specification Version 2.0. The USB
host initiates all USB data transfers to and from the NET2270 USB port. The NET2270 can be configured for up to
3 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 NET2270 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 NET2270 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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