LAN89730 datasheet(33/218 Pages) MICROCHIP

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DS60001348A-page 33

LAN89730

4.3.1.2

Endpoint 2 (Bulk-Out)

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

net 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 exist. This means that the current Bulk-Out packet was accepted, but room does not

exist for a second packet. If less than 512 bytes exist, the URX responds with a NACK. The URX supports the PING

protocol.

In the case where the Bulk-Out packet is errored, the URX does not respond to the host. The URX will request that the

FCT rewinds the packet. It is the host’s responsibility to retransmit the packet at a later time.

The FCT notifies the URX when it detects loss of sync. When this occurs, the URX stalls the Bulk-Out pipe. This is an

appropriate response, as loss of sync is a catastrophic error. This behavior is configurable via the Stall Bulk-Out Pipe

Disable (SBP) bit of the Hardware Configuration Register (HW_CFG) on page 123.

FIGURE 4-3:

USB BULK-OUT TRANSACTION SUMMARY

Host

Function

Out Token

Data Out

Transfer

ACK

NYET

STALL

Ping

Data Error

ACK

NAK

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