XR22417 Datasheet, PDF (9/17 Pages) Exar Corporation – USB 2.0 7-Port Hub

XR22417
Applications Information (Continued)
External EEPROM
An external I²C EEPROM may be used with the XR22417 to configure USB device descriptors, the number of
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
0x00
0x01
0x02
0x03
0x04
0x05
0x06
0x07
0x08 to 0x17
0x18
0x19
0x1A
0x1B
0x1C
0x1D
0x1E
0x1F
Content
0x40
0x1A
Vendor ID, LSB
Vendor ID, MSB
Product ID, LSB
Product ID, MSB
Device Release, LSB
Device Release, MSB
Device Serial Number
Serial Number Length
0x00
Downstream Ports
0x00
Device Removable
0x00
Device Attributes
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.
ASCII alpha-numeric serial number with maximum length 16 characters. First character of
serial number string in location 0x08.
Length of device serial number.
Reserved.
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.
Reserved.
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.
Reserved.
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.
Bitwise checksum of EEPROM values from address 0x00 to 0x1E.
REV1A
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