XR

22417

10/17

REV1A

Applications Information (Continued)

Configurations for Reduced Downstream Ports

The number of usable downstream ports of the XR22417 may be configured using an external EEPROM. Additionally,

the number of usable downstream ports may be reduced from 7 down to a minimum of 4 by strapping options on the device,

shown in Table 2. Both the EEPROM values and the strapping options will change the bNbrPorts field of the hub descriptor

reported to the USB host. LED pins for unusable downstream ports are disabled.

Table 2: Strapping Options for Reducing Usable Downstream Ports

Usable Downstream Ports

LED7

LED6

4, 3, 2, 1

Logic ‘0’

Logic ‘0’

5, 4, 3, 2, 1

Normal

Logic ‘0’

6, 5, 4, 3, 2, 1

Logic ‘0’

Normal

7, 6, 5, 4, 3, 2, 1

Normal

Normal

Configurations for Non-Removable Devices

Non-removable devices are reported in the device removable field of the hub descriptor. They can be identified by

strapping options. LED pins for non-removable downstream ports are disabled.

Table 3: Strapping Options for Configuring Non-Removable Downstream Ports

Non-Removable Downstream Ports

LED4

LED3

LED2

None

Normal

Normal

Normal

2

Normal

Normal

Logic ‘0’

3, 2

Normal

Logic ‘0’

Normal

3, 2, 1

Normal

Logic ‘0’

Logic ‘0’

4, 3, 2, 1

Logic ‘0’

Normal

Normal

5, 4, 3, 2, 1

Logic ‘0’

Normal

Logic ‘0’

6, 5, 4, 3, 2, 1

Logic ‘0’

Logic ‘0’

Normal

7, 6, 5, 4, 3, 2, 1

Logic ‘0’

Logic ‘0’

Logic ‘0’