AX88141 datasheet(29/43 Pages) ASIX

29 / 43 page

AX88141

PRELIMINARY

ASIX ELECTRONICS CORPORATION

CONFIDENTIAL

5.2 Receive Descriptors

The receive descriptor provides one buffer, one byte-count buffer, and one address pointer in

each descriptor. Descriptors and receive buffers addresses must be long-word aligned.

Receive Descriptor Format

RDES0

Status

RDES1

Control bits

Byte Count Buffer 2

Byte Count Buffer 1

RDES2

Buffer Address 1

RDES3

Buffer Address 2

Fig - 4 Receive Descriptor Format

5.2.1 Receive Descriptor 0 (RDES0)

RDES0 contains the received frame status, the frame length, and the descriptor ownership

information.

Field

Description

Indicates that the descriptor is owned by the AX88141

OWN - Own Bit

The AX88141 clears this bit either when it completes the

frame reception or

when the buffers that are associated with this descriptor are

full.

Indicates that the descriptor is owned by the host

Indicates that the frame failed the address recognition filtering

FF - Filtering Fail

This bit can be set only when receive all (REG6<30>) is set.

Indicates that the frame passed the address recognition filtering

29:16

FL - Frame Length

Indicates the length in bytes of the received frame including the cyclic redundancy check (CRC).

This field is valid only when last descriptor (RDES0<8>) is set and descriptor error ( RDES0<14>) is reset.

ES - Error Summary

Indicates the logical OR of the following RDES0 bits :

This field is valid only when last descriptor (RDES0<8>) is set.

RDES0<1>

CRC error

RDES0<6>

collision seen

RDES0<7>

frame too long

RDES0<11>

runt frame

RDES0<14>

descriptor error

DE - Descriptor Error. The frame is truncated. Active high.

This field is valid only when last descriptor (RDES0<8>) is set.

13:12

Reserved.--Written as “0” for future compatibility concern.

RF - Runt Frame. Indicates that this frame is a runt frame. Active high.

This field is valid only when last descriptor (RDES0<8>) is set .

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