USB2524 datasheet(43/58 Pages) MICROCHIP

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 2013 - 2016 Microchip Technology Inc.

DS00001588B-page 43

USB2524

9.0

RESET

9.1

Reset

There are two different resets that the Hub experiences. One is a hardware reset (via the RESET_N pin) and the second

is a USB Bus Reset.

9.1.1

EXTERNAL HARDWARE RESET_N

A valid hardware reset is defined as, assertion of RESET_N for a minimum of 1us after all power supplies are within

operating range. While reset is asserted, the Hub (and its associated external circuitry) consumes less than 500

A of

current from the upstream USB power source (300

A for the Hub and 200A for the external circuitry).

Assertion of RESET_N (external pin) causes the following:

• All downstream ports are disabled, and PRTPWR power to downstream devices is removed.

• The PHYs are disabled, and the differential pairs will be in a high-impedance state.

• All transactions immediately terminate; no states are saved.

• All internal registers return to the default state (in most cases, 00(h)).

• The external crystal oscillator is halted.

• The PLL is halted.

• LED indicators are disabled.

The Hub is “operational” 500

s after RESET_N is negated.

Once operational, the Hub immediately reads OEM-specific data from the external EEPROM (if the SMBus option is not

disabled) or the internal ROM.

9.1.1.1

RESET_N for Strapping Option Configuration

FIGURE 9-1:

RESET_N TIMING FOR DEFAULT/STRAP OPTION MODE

Valid

Don’t Care

Driven by Hub if strap is an output.

RESET_N

VSS

Strap Pins

VSS

Hardware

reset

asserted

Read Strap

Options

Drive Strap

Outputs to

inactive

levels

Attach

USB

Upstream

USB Reset

recovery

Idle

Start

completion

request

response

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