ISP1122A Просмотр технического описания (PDF) - Philips Electronics

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ISP1122A

Universal Serial Bus stand-alone hub

Philips Electronics 

Philips Semiconductors

ISP1122A

USB stand-alone hub

8. 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).

Table 5: Hub endpoints

Function Ports

0: upstream

Hub

1 to 5: downstream

Endpoint Transfer

identifier type

0

control

1

interrupt

Direction [1] Max. packet

size (bytes)

OUT

64

IN

64

IN

1

[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).

9397 750 06986

Preliminary specification

Rev. 01 — 27 March 2000

© Philips Electronics N.V. 2000. All rights reserved.

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