LAN89218 datasheet(47/148 Pages) MICROCHIP

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DS60001255B-page 47

LAN89218

3.12.2.1

TX Command ‘A’

TABLE 3-13:

TX COMMAND 'A' FORMAT

Bits

Description

Interrupt on Completion. When set, the TXDONE flag will be asserted when the current buffer has

been fully loaded into the TX FIFO. This flag may be optionally mapped to a host interrupt.

30:26

Reserved. These bits are reserved. Always write zeros to this field to guarantee future compatibility.

25:24

Buffer End Alignment. This field specifies the alignment that must be maintained on the last data

transfer of a buffer. The host will add extra DWORDs of data up to the alignment specified in the table

below. The LAN89218 will remove the extra DWORDs. This mechanism can be used to maintain cache

line alignment on host processors.

23:21

Reserved. These bits are reserved. Always write zeros to this field to guarantee future compatibility

20:16

Data Start Offset (bytes). This field specifies the offset of the first byte of TX data. The offset value can

be anywhere from 0 bytes to 31 a Byte offset.

15:14

Reserved. These bits are reserved. Always write zeros to this field to guarantee future compatibility

First Segment (FS). When set, this bit indicates that the associated buffer is the first segment of the

packet.

Last Segment. When set, this bit indicates that the associated buffer is the last segment of the packet

Reserved. These bits are reserved. Always write zeros to this field to guarantee future compatibility.

10:0

Buffer Size (bytes). This field indicates the number of bytes contained in the buffer following this com-

mand. This value, along with the Buffer End Alignment field, is read and checked by the LAN89218 and

used to determine how many extra DWORDs were added to the end of the Buffer. A running count is

also maintained in the LAN89218 of the cumulative buffer sizes for a given packet. This cumulative

value is compared against the Packet Length field in the TX command ‘B’ word and if they do not cor-

relate, the TXE flag is set.

Note:

The buffer size specified does not include the buffer end alignment padding or data start off-

set added to a buffer.

[25]

[24]

End Alignment

4-byte alignment

16-byte alignment

32-byte alignment

Reserved

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