GL850 datasheet(27/40 Pages) ETC

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GL850 USB 2.0 4-Port HUB Controller

Page 27

5.4 Descriptors

Descriptors contain all the information about the USB2.0 hub. Host asks different types of descriptors by

different GET_DESCRIPTOR commands. Hub will reply to different GET_DESCRIPTOR the associated

descriptors to let host know how to configure the hub. For an USB2.0 hub, the descriptors are:

Device Descriptor

Device Qualifier Descriptor

Configuration Descriptor

Interface Descriptor

Endpoint Descriptor

Other Speed Configuration Descriptor

Hub Class-specific Descriptor

String Descriptor

Descriptors replied are different between full speed and high speed for an USB2.0 hub. Once an USB2.0

hub is plugged into a host/hub, it needs to firstly decide the host/hub is an USB1.1 host/hub or an

USB2.0 host/hub. If the host/hub being plugged is an USB1.1 hub, GL850 replies to the host the full

speed descriptors defined in section 6.2.1. Otherwise, GL850 replies the high speed descriptors defined

in section 6.2.2. For hub class-specific descriptor, there’s no difference between full speed and high speed.

5.4.1 Full Speed Case

5.4.1.1 Device Descriptor

Hub returns Device Descriptor when GET_DESCRIPTOR (DEVICE) command is requested.

Table 5.4 - Device Descriptor for Full Speed

Offset

Field

Value

Description

I/O

Configuration

EEPROM

Configuration

bLength

12h

18 bytes for this descriptor

bDescriptorType

01h

Device descriptor type

bcdUSB

0200h USB2.0 compliance

bDeviceClass

09h

Hub class code

bDeviceSubClass

00h

Subclass code

bDeviceProtocol

00h

Protocol code

bMaxPacktSize0

40h

Max. packet size of

endpoint0

idVendor

05E3h

Vendor ID of Genesys

Logic Inc.

idProduct

0660h

Product ID of Genesys

Logic Inc.

bcdDevice

xxxxh Version Control

iManufacturer

00h

Index of vendor string

idProduct

01h

Index of product string

iSerialNumber

00h

Index of serial number

bNumConfigurations

01h

Number of configuration

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