lan9220 Standard Microsystems Corp., lan9220 Datasheet - Page 51

• Manufacturer Part Number: lan9220
• Description: 16-bit Non-pci Small Form Factor 10/100 Ethernet Controller With Variable Voltage I/o & Hp Auto-mdix Support
• Manufacturer: Standard Microsystems Corp.

16-bit Non-PCI Small Form Factor 10/100 Ethernet Controller with Variable Voltage I/O & HP Auto-MDIX Support
Datasheet
SMSC LAN9220
3.12.2
Figure 3.14, "TX Buffer
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
"Calculating Actual TX Data FIFO Usage," on page 55
actual TX data FIFO usage.
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 associated 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.
Host Write
Order
2nd
3rd
Last
1st
Format", shows the TX Buffer as it is written into the LAN9220. It should be
Figure 3.14 TX Buffer Format
31
Offset + Data DWORD0
Optional offset DWORD0
Optional offset DWORDn
DATASHEET
Optional Pad DWORDn
Optional Pad DWORD0
TX Command 'B'
TX Command 'A'
Last Data & PAD
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for a detailed explanation on calculating the
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Revision 2.6 (12-04-08)
Section 3.12.5,