LAN9500AI datasheet(28/213 Pages) MICROCHIP

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LAN950x

DS00001875A-page 28

 2010 - 2015 Microchip Technology Inc.

5.3.1.2

Endpoint 2 (Bulk Out)

The Bulk Out Endpoint is controlled by the URX (USB Bulk Out Receiver). The URX is responsible for receiving Ethernet

data encapsulated over a USB Bulk Out packet. Unlike the UTX, the URX does not explicitly track Ethernet frames. It

views all received packets as purely USB data. The extraction of Ethernet frames is handled by the FCT and the Trans-

action Layer Interface (TLI).

The URX always simultaneously supports multiple Ethernet frames per USB packet, as well as a single Ethernet frame

per USB packet. No mechanism exists to select between modes.

The URX monitors the amount of free space in the TX FIFO. If at least 512 bytes of space exists, the URX can accept

an additional Bulk In frame and responds to a Bulk Out Token with an ACK or NYET. The NYET response is used when

less than 1024 bytes of free space exists. This means that the current Bulk Out packet was accepted, but room does

not exist for a second packet. If less than 512 bytes exists, the URX responds with a NAK. The URX supports the PING

protocol.

FIGURE 5-2:

USB BULK IN TRANSACTION SUMMARY

In Token

Data In Transfer

Ack

Zero Length

Packet Transfer

Stall

Data Error

In Token Error

Host

Function

FS/HS

HS Only

Ack

LAN9500AI Datasheet(PDF) 28 Page - Microchip Technology