TUSB6250 datasheet(23/124 Pages) TI

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Architecture Overview

5−4

SLLS535A − January 2004

TUSB6250

5.2.6 I2C Interface Controller

The master-only I2C interface controller is responsible for acquiring the user configurable descriptors and

other configurable feature parameters from the external I2C EEPROM during initial power up. It is also used

to download the application firmware from the external I2C EEPROM. The behavior of the I2C interface

controller is controlled by the boot code (the microcode embedded in boot ROM) or application firmware.

5.3

Other Major Features

5.3.1 Unique Power-On Sequencing to the Storage Device

The TUSB6250 provides unique power-on sequencing features to the storage device. When the TUSB6250

is powered up during the reset period, it turns off all the output buffers and activates all of the internal pulldown

resistors on the ATA/ATAPI bus. After reset, when the TUSB6250 controller is enumerated and configured,

the application firmware in operation decides when to power up the connected ATA/ATAPI drive and

reconfigure all the input, output, and bidirectional buffers, and the pullup and pulldown resistors on the

ATA/ATAPI bus based on their functionality defined in the ATA/ATAPI-5 specification.

This function is critical for implementing a truly bus-powered USB 2.0 mass storage device, since the disk

start-up spinning normally results in a high-current surge that is harmful to the USB device during enumeration.

According to the USB 2.0 specification, a USB device is only allowed to consume up to 100 mA before it is

configured.

This feature is also useful when the TUSB6250 controller interfaces to ATA/ATAPI mass storage devices that

do not implement fail-safe buffers on their ATA/ATAPI interface. In such conditions, this well controlled

power-on sequencing feature protects the connected storage device without fail-safe I/O buffers from

damage, which may be caused by the bridge controller driving the signal lines when the power supply of the

storage devices is not present.

5.3.2 Die-ID Based USB Device Serial Number

The TUSB6250 supports unique USB device serial numbers by utilizing the 48-bit die-ID number unique to

each silicon die. It also allows end product developers to specify their own custom serial number in the external

I2C EEPROM to override this default die-ID serial number.

TUSB6250 датащи(PDF) 23 Page - Texas Instruments