XR

22417

9/17

REV1A

Applications Information (Continued)

External EEPROM

downstream ports, a device serial number, and downstream non-removable devices. The contents of the EEPROM are

described in Table 1. In order for contents of the EEPROM to be used by the XR22417, both the EEPROM check values at

address 0x00, 0x01 and the checksum at address 0x1F must be correct. If either field is incorrect, the EEPROM contents

will be ignored and the device will use the default descriptor values. Note that using the EEPROM requires the use of

serial numbers. By USB specification, if the hub is serialized, each individual device must be guaranteed to have a unique

serial number.

Table 1: EEPROM Contents

Address

Content

Description

0x00

0x40

EEPROM check value.

0x01

0x1A

EEPROM check value.

0x02

Vendor ID, LSB

idVendor field LSB of device descriptor.

0x03

Vendor ID, MSB

idVendor field MSB of device descriptor.

0x04

Product ID, LSB

idProduct field LSB of device descriptor.

0x05

Product ID, MSB

idProduct field MSB of device descriptor.

0x06

Device Release, LSB

bcdDevice field LSB of device descriptor in binary coded decimal format.

0x07

Device Release, MSB

bcdDevice field MSB of device descriptor in binary coded decimal format.

0x08 to 0x17

Device Serial Number

ASCII alpha-numeric serial number with maximum length 16 characters. First character of

serial number string in location 0x08.

0x18

Serial Number Length

Length of device serial number.

0x19

0x00

Reserved.

0x1A

Downstream Ports

Number of downstream ports in the bNbrPorts field of the hub descriptor. EEPROM value

will take precedence over any strapping options from Table 2 and Table 3.

0x1B

0x00

Reserved.

0x1C

Device Removable

Device removable field of hub descriptor. Bit n = ‘0’ indicates a removable device, or bit n =

‘1’ indicates a non-removable device for port n, (n = port 1 - 7). Bit 0 is reserved. EEPROM

value will take precedence over any strapping options from Table 2 and Table 3.

0x1D

0x00

Reserved.

0x1E

Device Attributes

Bit 0: port indicators support, bit 7 of wHubCharacteristics field of hub descriptor - 0: port

indicators are not supported on its downstream facing ports and PORT_ INDICATOR

request has no effect. 1: port indicators are supported on its downstream facing ports and

PORT _INDICATOR request controls the indicators.

Bit 1: identifies a compound device, bit 2 of wHubCharacteristics field of hub descriptor - 0:

hub is not part of a compound device. 1: hub is part of a compound device.

Bit 2: maximum current requirements of the hub controller electronics, bHubContrCurrent

field of hub descriptor - 0: 200 mA. 1: 500 mA.

Bit 3 to 7, reserved, must be 0’s.

0x1F

Checksum

Bitwise checksum of EEPROM values from address 0x00 to 0x1E.