USB251XB datasheet(22/57 Pages) MICROCHIP

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USB251xB/xBi

DS00001692D-page 22

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5.1.7

Bit Number

Bit Name

Description

SELF_BUS_PWR

Self or Bus Power: selects between self- and bus-powered operation.

The hub is either self-powered (draws less than 2 mA of upstream bus power)

or bus-powered (limited to a 100 mA maximum of upstream power prior to

being configured by the host controller).

When configured as a bus-powered device, the hub consumes less than

100 mA of current prior to being configured. After configuration, the bus-

powered hub, along with all associated hub circuitry, any embedded devices

(if part of a compound device), and all externally available downstream ports

(max 100 mA) must consume no more than 500 mA of upstream VBUS

current. The current consumption is system dependent and must not violate

the USB 2.0 Specification [1].

When configured as a self-powered device, < 1 mA of upstream VBUS current

is consumed and all ports are available. Each port is capable of sourcing

500 mA of current.

This field is set over either the SMBus or I2C EEPROM interface options.

: bus-powered operation

: self-powered operation

If dynamic power switching is enabled (Section 5.1.8), this bit is ignored and

LOCAL_PWR is used to determine if the hub is operating from self or bus

power.

rsvd

HS_DISABLE

Hi-Speed Disable: disables the capability to attach as either a hi- or full-speed

device, forcing full-speed attachment only (i.e., no hi-speed support).

: hi-/full-speed

: full-speed only (hi-speed disabled)

MTT_ENABLE

Multi-TT Enable: enables one transaction translator per port operation.

Selects between a mode where only one transaction translator is available for

all ports (single-TT), or each port gets a dedicated transaction translator

(multi-TT).

: single TT for all ports

: multi-TT (one TT per port)

EOP_DISABLE

EOP Disable: disables End Of Packet (EOP) generation at End Of Frame

Time #1 (EOF1) when in full-speed mode.

During full-speed operation only, the hub can send EOP when no downstream

traffic is detected at EOF1. See the USB 2.0 Specification, Section 11.3.1 for

details.

: EOP generation is normal

: EOP generation is disabled

2:1

CURRENT_SNS

Over-Current Sense: selects current sensing on all ports (ganged); a port-by-

port basis (individual); or none (for bus-powered hubs only). The ability to

support current sensing on a ganged or port-by-port basis is hardware

implementation dependent.

: ganged sensing

: individual sensing

: over-current sensing not supported (use with bus-powered configurations)

PORT_PWR

Port Power Switching: enables power switching on all ports (ganged) or a port-

by-port basis (individual). The ability to support power enabling on a ganged

or port-by-port basis is hardware implementation dependent.

: ganged switching

: individual switching

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