USB2504 datasheet(33/46 Pages) SMSC

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Integrated USB 2.0 Compatible 4-Port Hub

Datasheet

SMSC USB2504/USB2504A

Revision 2.3 (08-27-07)

DATASHEET

5.3.9.17

5.3.9.18

Undefined Registers

The registers shown in Table 5.4 are the defined registers in the Hub. Reads to undefined registers

return 00h. Writes to undefined registers have no effect and do not return an error.

5.3.9.19

Reserved Registers

Unless otherwise instructed, only a ‘0’ may be written to all reserved registers or bits.

5.4

Default Configuration Option:

The SMSC Hub can be configured via its internal default configuration. (please see for specific details

on how to enable default configuration.

Please refer to Table 5.1 on page 20 for the internal default values that are loaded when this option is

selected.

5.5

Default Strapping Options:

The SMSC Hub can be configured via a combination of internal default values and pin strap options.

Please see Table 4.1, "7-Port Hub Pin Descriptions" for specific details on how to enable the

default/pin-strap configuration option.

The strapping option pins only cover a limited sub-set of the configuration options. The internal default

values will be used for the bits & registers that are not controlled by a strapping option pin. Please

refer to Table 5.1 on page 20 for the internal default values that are loaded when this option is selected.

The Amber and Green LED pins are sampled after RESET_N negation, and the logic values are used

to configure the hub if the internal default configuration mode is selected. The implementation shown

below (see Figure 5.1) shows a recommended passive scheme. When a pin is configured with a “Strap

High” configuration, the LED functions with active low signalling, and the PAD will “sink” the current

from the external supply. When a pin is configured with a “Strap Low” configuration, the LED functions

with active high signalling, and the PAD will “source” the current to the external LED.

BIT

NUMBER

BIT NAME

DESCRIPTION

7:0

POWER_ON_TIME

Power On Time: The length of time that it takes (in 2 ms intervals) from the

time the host initiated power-on sequence begins on a port until power is

good on that port.

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