LAN9250 datasheet(154/421 Pages) MICROCHIP

154 / 421 page

LAN9250

DS00001913A-page 154

 2015 Microchip Technology Inc.

Note:

When the TXCOE is enabled, the third DWORD of the prepended packet is not transmitted. However, 4

bytes must be added to the packet length field in TX Command B.

Note:

Software applications must stop the transmitter and flush the TX data path before changing the state of the

TXCOE_EN bit. However, the CK bit of TX Command B can be set or cleared on a per-packet basis.

Note:

The TXCOE_MODE may only be changed if the TX path is disabled. If it is desired to change this value

during run time, it is safe to do so only after the TX Ethernet path is disabled and the TLI is empty.

Note:

The TX checksum preamble must be DWORD-aligned.

Note:

TX preamble size is accounted for in both the buffer length and packet length.

Note:

The first buffer, which contains the TX preamble, may not contain any Ethernet frame data

Figure 11-8 illustrates the use of a prepended checksum preamble when transmitting an Ethernet frame consisting of 3

payload buffers.

TABLE 11-8:

TX CHECKSUM PREAMBLE

Field

Description

TXCSUDP - TX Checksum UDP Frame

This bit specifies if a checksum result of 0x0000 should be changed to 0xFFFF.

30:28

RESERVED

27:16

TXCSLOC - TX Checksum Location

This field specifies the byte offset where the TX checksum will be inserted in the TX packet. The

checksum will replace two bytes of data starting at this offset.

The TX checksum cannot be inserted in the MAC header (first 14 bytes) or in the last 4 bytes of the

TX packet.

15:12

RESERVED

11:0

TXCSSP - TX Checksum Start Pointer

This field indicates start offset, in bytes, where the checksum calculation will begin in the associated

TX packet.

The data checksum calculation must not begin in the MAC header (first 14 bytes) or in the last 4

bytes of the TX packet.

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