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Endpoint Descriptor

Each endpoint used for an interface has its own descriptor, which contains the information required by the host to determine

the bandwidth requirements of each endpoint (see Table 6). An endpoint descriptor, like an Interface Descriptor, is always

returned as part of a configuration descriptor. The default values are:

Bulk In 1:

07058102100000

Bulk Out 1:

07050102100000

Bulk In 2:

07058203080064

Bulk Out 2:

07050202080000

Table 6. Endpoint Descriptors

Offset

Field

Size

Value

Description

0

bLength

1

Number

Size of this descriptor in bytes.

1

bDescriptorType

1

Constant

ENDPOINT Descriptor Type.

2

bEndpointAddress

1

Endpoint

The address of the endpoint on the USB device described by this

descriptor. The address is encoded as follows:

Bit 0..3: The endpoint number

Bit 4..6: Reserved, reset to 0

Bit 7:

Direction, ignored for control endpoints

0

OUT endpoint

1

IN endpoint

3

bmAttributes

1

Bit Map

This field describes the endpoint’s attributes when it is configured using

the bConfigurationValue.

Bit 0..1: Transfer Type

00

Control

01

Isochronous

10

Bulk

11

Interrupt

All other bits are reserved

4

wMaxPacketSize

2

Number

Maximum packet size this endpoint is capable of sending or receiving

when this configuration is selected.

For isochronous endpoints, this value is used to reserve the bus time in

the schedule, required for the per frame data payloads. The pipe may,

on an ongoing basis, actually use less bandwidth than that reserved.

The device reports, if necessary, the actual bandwidth used via its

normal, non-USB defined mechanisms.

For interrupt, bulk, and control endpoints smaller data payloads may be

sent, but will terminate the transfer and may or may not require

intervention to restart. Refer to Chapter 5 for more information.

6

bInterval

1

Number

Interval for polling endpoint for data transfers. Expressed in

milliseconds.

This field is ignored for bulk and control endpoints. For isochronous

endpoints this field must be set to 1. For interrupt endpoints, this field

may range from 1 to 255.