USB2504/USB2504A

DS000002250A-page 14

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5.1.1.15

Dynamic Power

Controls the ability of the 4-Port Hub to automatically change from Self-Powered operation to Bus-Powered operation

if the local power source is removed or is unavailable (and from Bus-Powered to Self-Powered if the local power source

is restored). {Note: If the local power source is available, the 4-port Hub will always switch to Self-Powered operation.}

When Dynamic Power switching is enabled, the Hub detects the availability of a local power source by monitoring the

external SELF_PWR pin. If the Hub detects a change in power source availability, the Hub immediately disconnects and

removes power from all downstream devices and disconnects the upstream port. The Hub will then re-attach to the

upstream port as either a Bus-Powered Hub (if local-power in unavailable) or a Self-Powered Hub (if local power is avail-

able).

This field is set by the OEM using either the SMBus or EEPROM interface options.

5.1.1.16

Over-Current Timer

The time delay (in 2ms increments) for an over-current condition to persist before it is reported to the Host.

This field is set by the OEM using either the SMBus or EEPROM interface options.

5.1.1.17

Self-Powered Max Power

When in Self-Powered configuration, Sets value in 2mA increments.

This field is set by the OEM using either the SMBus or EEPROM interface options.

5.1.1.18

Bus-Powered Max Power

When in Bus-Powered configuration, Sets value in 2mA increments.

This field is set by the OEM using either the SMBus or EEPROM interface options.

5.1.1.19

Self-powered Hub Controller Current

When in Self-Powered configuration, Maximum current requirements of the Hub Controller in 2mA increments.

This field is set by the OEM using either the SMBus or EEPROM interface options.

5.1.1.20

Bus-Powered Hub Controller Current

When in Bus-Powered configuration, Maximum current requirements of the Hub Controller in 2mA increments.

This field is set by the OEM using either the SMBus or EEPROM interface options.

5.1.1.21

Power-On Timer

Time (in 2ms intervals) from the time power-on sequence begins on a port until power is good on that port. System soft-

ware uses this value to determine how long to wait before accessing a powered-on port.

This field is set by the OEM using either the SMBus or EEPROM interface options.

5.1.1.22

Power Switching Polarity

The selection of active state “polarity” for the PRTPWR[4:1] pins is made by a strapping option only.

5.1.2

VBUS DETECT

According to Section 7.2.1 of the USB 2.0 Specification, a downstream port can never provide power to its D+ or D- pull-

up resistors unless the upstream port’s VBUS is in the asserted (powered) state. The VBUS_DET pin on the Hub mon-

itors the state of the upstream VBUS signal and will not pull-up the D+ or D- resistor if VBUS is not active. If VBUS goes

from an active to an inactive state (Not Powered), Hub will remove power from the D+ or D- pull-up resistor within 10

seconds.

5.2

EEPROM Interface

The Internal state-machine will, (when configured for EEPROM support) read the external EEPROM for configuration

data. The hub will then “attach” to the upstream USB host.

Please see Table 5-1 User-Defined Descriptor Data for a list of data fields available.