LAN9730 datasheet(40/222 Pages) MICROCHIP

40 / 222 page

LAN9730/LAN9730i

DS00001946A-page 40

 2012-2015 Microchip Technology Inc.

Note 4-13

Value is loaded from EEPROM, but must be equal to the default value in order to comply with the USB

2.0 Specification and provide for normal device operation. Specification of any other value will result

in unwanted behavior and untoward operation.

4.3.1.6.9

String Descriptors

String Index = 0 (LANGID)

String Indices 1-5

Note:

EEPROM values are from the Device Descriptor (including any EEPROM override) at the opposite HS/FS

operating speed. I.e., if the current operating speed is HS, then Device Qualifier data is based on the FS

Device Descriptor, and vice-versa.

TABLE 4-12:

LANGID STRING DESCRIPTOR

Offset

Field

Size

(Bytes)

Default

Value

Loaded

from

EEPROM

Description

00h

bLength

04h

Size of LANGID Descriptor in bytes

(4 bytes)

01h

bDescriptorType

03h

String Descriptor (0x03)

02h

LANGID

None

Yes

Must be set to 0x0409 (US English).

Note:

If there is no valid/enabled EEPROM, or if all string lengths in the EEPROM are 0, then there are no strings,

so any host attempt to read the LANGID string will return stall in the Data Stage of the Control Transfer.

If there is a valid/enabled EEPROM, and if at least one of the string lengths in the EEPROM is not 0, then

the value contained at EEPROM addresses 0x0A-0x0B will be returned. These must be 0x0409 to allow

for proper device operation.

Note:

The device ignores the LANGID field in Control Read’s of Strings, and will not return the String (if it exists),

regardless of whether the requested LANGID is 0x0409 or not.

TABLE 4-13:

STRING DESCRIPTOR (INDICES 1-5)

Offset

Field

Size

(Bytes)

Default

Value

Loaded

from

EEPROM

Description

00h

bLength

none

Yes

Size of the String Descriptor in bytes

(4 bytes)

01h

bDescriptorType

none

Yes

String Descriptor (0x03)

02h

Unicode String

2*N

none

Yes

2 bytes per unicode character, no trail-

ing NULL.

Note:

If there is no valid/enabled EEPROM, or if the corresponding String Length and offset in the EEPROM for

a given string index are zero, then that string does not exist, so any host attempt to read that string will

return stall in the Data Stage of the Control Transfer.

Note:

The device returns whatever bytes are in the designated EEPROM area for each of these strings. It is the

responsibility of the EEPROM programmer to correctly set the bLength and bDescriptorType fields in the

descriptor consistent with the byte length specified in the corresponding EEPROM locations.

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