AX88796BLF datasheet(18/82 Pages) ASIX

18 / 82 page

ASIX ELECTRONICS CORPORATION

AX88796BLF / AX88796BLI

4.2.2 Packet Transmission

The Local DMA Read is also used during transmission of a packet. Three registers control the DMA transfer during

transmission, a Transmit Page Start Address Register (TPSR) and the Transmit Byte Count Registers (TBCR0, 1).

When the AX88796B receives a command to transmit the packet pointed to by these registers, buffer memory data

will be moved into the FIFO as required during transmission. The AX88796B Controller will generate and append

the preamble, synch and CRC fields. AX88796B supports options of transmit queue function to enhance transmit

performance.

Original NE2000 Of Transmit Buffer

Options Of Transmit Buffer As A Ring

Options Back-To-Back Transmission (TX Command Queue)

TPSR

TBCR

1, 0

TX Page Start Address (0x40)

Transmit buffer

Receive buffer

AX88796B

remote

DMA

write

default

operation

continue to write next address

even over transmit buffer

area. Host can do whole

memory read / write testing.

And host must handle the

transmit data do not overwrite

receive

buffer

area

when

performing fill transmit data

to transmit buffer.

TX Page Start Address (0x40)

Transmit buffer

Receive buffer

When active Transmit Buffer

Ring Enable (CR page3 of

offset

0Dh).

AX88796B

remote DMA write operation

will

role

over

from

last

transmit page to first transmit

page. Host no need reassign

RSAR0, RSAR1 again to fill

transmit data for first page.

Rx Page Start Register,

PSTART (CR page0, offset

01h)

Rx Page Start Register,

PSTART (CR page0, offset

01h)

TX Command Queue

Push In

Pop Out

When active TX Queue Enable

(offset 1Bh), Host can continue

Writing TXP (bit 2 of CR

TBCR1, 0 into AX88796B TX

command queue as long as

Transmit buffer has enough

vacancy and

CTEPR (offset

1Ch) bit7 is ‘0’(Not full). After

current

packet

transmitted

completely, MAC TX will pop

out next TPSR and TBCR1, 0

from TX Command Queue

then

transmit

this

packet

following CSMA/CD protocol.

It is recommended to enable

this function to enhance TX

performance.

AX88796B will report Current of Transmit End Page

CTEPR (offset 1Ch) when every packet transmits

completed.

Host can understand AX88796B current of transmitting

buffer point by reading CTEPR.

MAC TX

function block

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