AX88796LF datasheet(26/71 Pages) ASIX

26 / 71 page

ASIX ELECTRONICS CORPORATION

AX88796 L

3-in-1 Local Bus Fast Ethernet Controller

Destination Address

6 Bytes

Source Address

6 Bytes

Length / Type

2 Bytes

Data

(Pad if < 46 Bytes)

46 Bytes

Min.

General Transmit Packet Format

TRANSMISSION

Prior to transmission, the TPSR (Transmit Page Start Register) and TBCR0, TBCR1 (Transmit Byte Count

Registers) must be initialized. To initiate transmission of the packet the TXP bit in the Command Register is set.

The Transmit Status Register (TSR) is cleared and the AX88796 begins to prefetch transmit data from memory.

If the Interpacket Gap (IPG) has timed out the AX88796 will begin transmission.

CONDITIONS REQUIRED TO BEGIN TRANSMISSION

In order to transmit a packet, the following three conditions must be met:

1. The Interpacket Gap Timer has timed out

2. At least one byte has entered the FIFO. (This indicates that the burst transfer has been started)

3. If a collision had been detected then before transmission the packet backoff time must have timed out.

COLLISION RECOVERY

During transmission, the Buffer Management logic monitors the transmit circuitry to determine if a collision has

occurred. If a collision is detected, the Buffer Management logic will reset the FIFO and restore the Transmit

DMA pointers for retransmission of the packet. The COL bit will be set in the TSR and the NCR (Number of

Collisions Register) will be incremented. If 15 retransmissions each result in a collision the transmission will be

aborted and the ABT bit in the TSR will be set.

Transmit Packet Assembly Format

The following diagrams describe the format for how packets must be assembled prior to transmission for

different byte ordering schemes. The various formats are selected in the Data Configuration Register and setting

the CPU[1:0] pins for ISA, 80186, MC68K or MCS-51 mode.

D15

Destination Address 1

Destination Address 0

Destination Address 3

Destination Address 2

Destination Address 5

Destination Address 4

Source Address 1

Source Address 0

Source Address 3

Source Address 2

Source Address 5

Source Address 4

Type / Length 1

Type / Length 0

Data 1

Data 0

…

BOS = 0, WTS = 1 in Data Configuration Register.

This format is used with ISA or 80186 Mode.

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