4-Port USB 2.0 Hub Controller
Datasheet
Revision 1.63 (03-30-07)
Page 28
SMSC USB20H04
DATASHEET
Chapter 9
Hub Descriptors
The USB20H04 will not electrically attach to the USB until after it has loaded valid data for all user-defined
descriptor fields. A default configuration is present immediately after RESET_N negation. User defined
configuration values can be loaded from either an external microcontroller or an external EEPROM.
A hub returns different descriptors based on whether it is operating at high-speed or full-/low-speed. A hub
can report three different sets of the descriptors: one descriptor set for full-/low-speed operation and two
sets for high-speed operation. The descriptors reported by the USB20H04 are summarized in the following
tables. The host retrieves this information by using the GetDescriptor request with the corresponding
descriptor type values.
Table 9.1 - Device Descriptor
OFFSET
FULL
SPEED
HIGH
SPEED
FIELD NAME
DESCRIPTION
0 12h 12h
bLength
Size of this descriptor in bytes
1 01h 01h
bDescriptorType
DEVICE Descriptor Type
2,3 0200h 0200h
bcdUSB
USB Specification Number
4 09h 09h
bDeviceClass
Class code assigned by USB-IF for Hubs
5 00h 00h
bDeviceSubClass
Class code assigned by USB-IF for Hubs
6 00h 01h*
bDeviceProtcol
Protocol code assigned by the USB-IF
7 40h 40h
bMaxPacketSize0
64-byte packet size
8,9 user user
idVendor
Vendor ID; OEM value
10,11 user
user
idProduct
Product ID; OEM value
12,13 user
user
bcdDevice
Device ID; OEM value
14 00h 00h
iManufacturer
This optional string is not supported.
15 00h 00h
iProduct
This optional string is not supported.
16 00h 00h
iSerialNumber
This optional string is not supported.
17 01h 01h
iNumConfigurations
Supports 1 configuration
* 02h for multiple-TT
Table 9.2 - Device Qualifier Descriptor
OFFSET
FULL
SPEED
HIGH
SPEED
FIELD NAME
DESCRIPTION
0 0Ah 0Ah
bLength
Size of this descriptor in bytes
1 06h 06h
bDescriptorType
DEVICE Qualifier Type
2 00h 00h
bcdUSB
USB Specification Version Number (LSB)
3 02h 02h
bcdUSB
USB Specification Version Number (MSB)
4 09h 09h
bDeviceClass
Class code assigned by USB-IF for Hubs
5 00h 00h
bDeviceSubClass
Class code assigned by USB-IF for Hubs
Protocol code.
6 00h 01h*
bDeviceProtcol
7 40h 40h
bMaxPacketSize0
64-byte packet size for other speed
8 01h 01h
bNumConfigurations
Supports 1 other speed configuration
9 00h 00h
bReserved
Reserved
* 02h for multiple-TT
