LAN9220 datasheet(42/142 Pages) MICROCHIP

42 / 142 page

LAN9220

DS00002417A-page 42

 2006-2017 Microchip Technology Inc.

3.12.1

TX BUFFER FORMAT

TX buffers exist in the host’s memory in a given format. The host writes a TX command word into the TX data buffer

before moving the Ethernet packet data. The TX command A and command B are 32-bit values that are used by the

LAN9220 in the handling and processing of the associated Ethernet packet data buffer. Buffer alignment, segmentation

and other packet processing parameters are included in the command structure. The following diagram illustrates the

buffer format.

Figure 3-20, "TX Buffer Format", shows the TX Buffer as it is written into the LAN9220. It should be noted that not all of

the data shown in this diagram is actually stored in the TX data FIFO. This must be taken into account when calculating

the actual TX data FIFO usage. Please refer to Section 3.12.5, "Calculating Actual TX Data FIFO Usage," on page 46

for a detailed explanation on calculating the actual TX data FIFO usage.

3.12.2

TX COMMAND FORMAT

The TX command instructs the TX FIFO controller on handling the subsequent buffer. The command precedes the data

to be transmitted. The TX command is divided into two, 32-bit words; TX command ‘A’ and TX command ‘B’.

There is a 16-bit packet tag in the TX command ‘B’ command word. Packet tags may, if host software desires, be unique

for each packet (i.e., an incrementing count). The value of the tag will be returned in the RX status word for the associ-

ated packet. The Packet tag can be used by host software to uniquely identify each status word as it is returned to the

host.

Both TX command ‘A’ and TX command ‘B’ are required for each buffer in a given packet. TX command ‘B’ must be

identical for every buffer in a given packet. If the TX command ‘B’ words do not match, the Ethernet controller will assert

the Transmitter Error (TXE) flag.

FIGURE 3-20:

TX BUFFER FORMAT

TX Command 'A'

Offset + Data DWORD0

Last Data & PAD

1st

2nd

3rd

Last

Host Write

Order

Optional Pad DWORD0

Optional Pad DWORDn

TX Command 'B'

Optional offset DWORD0

Optional offset DWORDn

LAN9220 датащи(PDF) 42 Page - Microchip Technology