USB2422

DS00001726B-page 16

4.0

CONFIGURATION OPTIONS

Microchip’s USB 2.0 hub is fully compliant with the USB Specification [1]. Refer to Chapter 10 (Hub Specification) for

general details regarding hub operation and functionality.

The hub provides one Transaction Translator (TT) that is shared by both downstream ports (defined as Single-TT con-

figuration). The TT contains 4 non-periodic buffers.

4.1

Hub Configuration

The USB2422 only supports internal defaults with the exception of the non-removable strap option (using

NON_REM[1:0]). The hub internal default settings are as follows:

• Internal Default Configuration without over-rides

• Strap options enabled

• Self-powered operation enabled

• Individual power switching

• Individual over-current sensing

4.2

Resets

There are two device resets: a hardware reset via RESET_N, and a USB Bus Reset.

4.2.1

EXTERNAL HARDWARE RESET_N

A valid hardware reset is defined as assertion of RESET_N for a minimum of 1

μs after all power supplies are within

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

μA of

current from the upstream USB power source.

Assertion of RESET_N causes the following:

1.

All downstream ports are disabled.

2.

The PRTPWR power to downstream devices is turned on when battery charging is enabled for a specific port,

and removed when battery charging is disabled for a specific port.

3.

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

4.

All transactions immediately terminate; no states are saved.

5.

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

6.

The external crystal oscillator is halted.

7.

The PLL is halted.

TABLE 4-1:

HUB CONFIGURATION OPTIONS

CFG_SEL

Description

0

Default configuration:

• Strap options enabled

• Hub descriptors indicate the hub as “self-powered”

1

The hub is configured externally over SMBus (as an SMBus slave

device with address 0101100b):

• Strap options disabled

• Self-powered or bus-powered depending on register settings

• All registers configured over SMBus