ISP1122ABD datasheet(11/48 Pages) PHILIPS

11 / 48 page

Philips Semiconductors

ISP1122A

USB stand-alone hub

Preliminary speciﬁcation

Rev. 01 — 27 March 2000

11 of 48

9397 750 06986

Endpoint descriptions

Each USB device is logically composed of several independent endpoints. An

endpoint acts as a terminus of a communication ﬂow between the host and the

device. At design time each endpoint is assigned a unique number (endpoint

identiﬁer, see Table 5). The combination of the device address (given by the host

during enumeration), the endpoint number and the transfer direction allows each

endpoint to be uniquely referenced.

The ISP1122A has two endpoints, endpoint 0 (control) and endpoint 1 (interrupt).

[1]

IN: input for the USB host; OUT: output from the USB host.

8.1 Hub endpoint 0 (control)

All USB devices and functions must implement a default control endpoint (ID = 0).

This endpoint is used by the host to conﬁgure the device and to perform generic USB

status and control access.

The ISP1122A hub supports the following USB descriptor information through its

control endpoint 0, which can handle transfers of 64 bytes maximum:

• Device descriptor

• Conﬁguration descriptor

• Interface descriptor

• Endpoint descriptor

• Hub descriptor

• String descriptor.

8.2 Hub endpoint 1 (interrupt)

Endpoint 1 is used by the ISP1122A hub to provide status change information to the

host. This endpoint can be accessed only after the hub has been conﬁgured by the

host (by sending the Set Conﬁguration command).

Endpoint 1 is an interrupt endpoint: the host polls it once every 255 ms by sending an

IN token. If the hub has detected no change in the port status it returns a NAK (Not

AcKnowledge) response to this request, otherwise it sends the Status Change byte

(see Table 6).

Table 5:

Hub endpoints

Function

Ports

Endpoint

identiﬁer

Transfer

type

Direction [1] Max. packet

size (bytes)

Hub

0: upstream

1 to 5: downstream

control

OUT

interrupt

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