AX88141

PRELIMINARY

ASIX ELECTRONICS CORPORATION

31

CONFIDENTIAL

5.3 Transmit Descriptors

Providing one buffer, one byte-count buffer, and two address pointers in each descriptor .

Transmit Descriptor Format

31

0

TDES0

O

W

N

Status

TDES1

Control bits

Byte Count Buffer 2

Byte Count Buffer 1

TDES2

Buffer Address 1

TDES3

Buffer Address 2

Fig - 5 Transmit Descriptor Format

5.3.1 Transmit Descriptor 0 (TDES0)

TDES0 contains transmitted frame status and descriptor ownership information.

Field

Description

1

Indicates that the descriptor is owned by the AX88141.

31

OWN - Own Bit

0

Indicates that the descriptor is owned by the host.

30:16

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

ES - Error Summary

Indicates the logical OR of the following bits :

TDES0<1>

under-flow error

TDES0<8>

successive collisions

TDES0<9>

late collision

TDES0<10>

no carrier

TDES0<11>

loss of carrier

15

TDES0<14>

transmit jabber time-out

14

TO - Transmit Jabber Time-out : Active high.

The transmission process is aborted and placed in the STOPPED state.

When TDES0<14> is set any heartbeat fail indication (TDES0<7>) is not valid.

13:12

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

11

LO - Loss of Carrier during transmission. Active high. (The status is no meaning except 10BASE SRL mode)

Not valid in internal loop-back mode (REG6<11:10>=01).

10

NC - No Carrier. Indicates that the carrier signal from the transceiver was not present during transmission. Active high.

Not valid in internal loop-back mode (REG6<11:10>=01).

9

LC - Late Collision. When set, indicates that the frame transmission was aborted due to collision occurring after the collision

window of 64 bytes. Not valid if under-flow error (TDES0<1>) is set.

8

EC - Excessive Collision When set, indicates that the transmission was aborted after 16 successive collisions while attempting to

transmit the current frame.

7

HF - Heartbeat Fail

This bit is effective only in 10Mb/s operation mode. When set, indicates a heartbeat collision check failure

This bit is not valid if under-flow error (TDES0<1>) is set.

On the second transmission attempt, after the first transmission was aborted due to collision, the AX88141 does not check

heartbeat fail and (TDES0<7>) is reset.

6:3

CC - Collision Count

This 4-bit counter indicates the number of collisions that occurred before the frame was transmitted.

Not valid when the excessive collisions bit (TDES0<8>) is also set.

2

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