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DS000002250A-page 29

USB2504/USB2504A

5.6.1.3

RESET_N for SMBus Slave Configuration

Note 1: For Bus-Powered configurations, the 99.5ms (MAX) is required, and the Hub and its associated circuitry

must not consume more than 100mA from the upstream USB power source during t2+t3+t4+t5+t6+t7. For

Self-Powered configurations, t3 MAX is not applicable and the time to load the configuration is determined

by the external SMBus host.

2: All Power Supplies must have reached the operating levels mandated in Section 8.0, "DC Parameters", prior

to (or coincident with) the assertion of RESET_N.

5.6.2

USB BUS RESET

In response to the upstream port signaling a reset to the Hub, the Hub does the following:

1.

Sets default address to 0.

2.

Sets configuration to: Unconfigured.

3.

Negates PRTPWR[4:1] to all downstream ports.

4.

Clears all TT buffers.

5.

Moves device from suspended to active (if suspended).

6.

Complies with Section 11.10 of the USB 2.0 Specification for behavior after completion of the reset sequence.

The Host then configures the Hub and the Hub’s downstream port devices in accordance with the USB Specification.

FIGURE 5-4:

RESET_N TIMING FOR SMBUS MODE

TABLE 5-7:

RESET_N TIMING FOR SMBUS MODE

Name

Description

MIN

TYP

MAX

Units

t1

RESET_N Asserted.

1

sec

t2

Hub Recovery/Stabilization.

500

sec

t3

SMBus Code Load (See Note).

10

99.5

msec

t4

Hub Configuration and USB Attach.

100

msec

t5

Host acknowledges attach and signals USB Reset.

100

msec

t6

USB Idle.

Undefined

msec

t7

Completion time for requests (with or without data

stage).

5

msec

Note:

The Hub does not propagate the upstream USB reset to downstream devices.

t1

t2

t4

t5

t6

t7

RESET_N

VSS

Hardware

reset

asserted

Reset

Negation

SMBus Code

Load

Attach

USB

Upstream

USB Reset

recovery

Idle

Start

completion

request

response

t3

Hub PHY

Stabilization