XR22404 Datasheet, PDF (9/14 Pages) Exar Corporation – USB 2.0 4-Port Hub

XR22404
Applications Information (Continued)
External EEPROM
An external I²C EEPROM may be used with the XR22404 to configure USB device descriptors and the number of
downstream ports. The contents of the EEPROM are described in Table 2. In order for contents of the EEPROM to be
used by the XR22404, both the EEPROM check values at address 0x00, 0x01 and the checksum at address 0x1F must be
correct. If either field is incorrect or reserved fields are not set to 0x00, the EEPROM contents will be ignored and the device
will use the default descriptor values.
Table 2. EEPROM Contents
Address
0x00
0x01
0x02
0x03
0x04
0x05
0x06
0x07
0x08 to 0x19
0x1A
0x1B to 0x1E
0x1F
Content
0x40
0x1A
Vendor ID, LSB
Vendor ID, MSB
Product ID, LSB
Product ID, MSB
Device Release, LSB
Device Release, MSB
Reserved
Downstream Ports
Reserved
Checksum
Description
EEPROM check value.
EEPROM check value.
idVendor field LSB of device descriptor.
idVendor field MSB of device descriptor.
idProduct field LSB of device descriptor.
idProduct field MSB of device descriptor.
bcdDevice field LSB of device descriptor in binary coded decimal format.
bcdDevice field MSB of device descriptor in binary coded decimal format.
Must be 0x00.
Number of downstream ports in the bNbrPorts field of the hub descriptor.
Must be 0x00.
Bitwise checksum of EEPROM values from address 0x00 to 0x1E.
REV1A
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