Sending and receiving Ethernet traffic

BTW, the statement about 4 pins is not correct.
I use 2 pins for transmission, but only 1 pin for reception (I have 2
transistors to create a differential input from the 10BASE-T RD+/RD- wires
to the FPGA).


we

we

Cool project. Have you coded the ethernet stuff by yourself or used an ip
block? You have one small misstake: The splitting in RX and TX lines on RJ45
does not prevent contention! It is still possible. Some time ago I was also
thinking about an ethernet inteface in an FPGA. I thought, like you, now
with RJ45 it's easier since contention detection is one of the hard parts.
However, if you read carefully the doc's it's still there ;-(

Martin

Martin,

about the contention, in the current IEEE spec (IEEE 802.3-2002), section
"4.2.3.2.6 Full duplex transmission" states:
"In full duplex mode, there is never contention for a shared physical
medium."

That's the beauty of it. Twice the bandwidth, and much easier to implement.
So my code is only intended to be connected to a full-duplex capable device
only (i.e. a switch or directly to another computer).

Your remark is true for half-duplex (which is much harder to implement!).
Hope that convinces you.
Jean


some
the
that
RJ45
also

Jean,

there is still a problem. If you use a point to point connection (with a
cross over cabel) it can be possible that both stations transmit without a
contention. However, Ethernet is still a bus. Imagine following situation:
Three stations (A,B,C) connected via a hub. Station A and B are sending at
the same time. Which message will arrive at C? This IS a contention. On A
and B perhaps you will not see a contention on the TX lines, however you
have to listen to the RX line while sending and abort your transmit, enter
the random timeout and retransmit.
And I'm not shure if a simple hub will support full duplex mode.

Sorry, I'm not convinced

Martin


implement.
device
it.
ip
parts.

On Tue, 09 Sep 2003 06:39:16 GMT, "Martin Schoeberl"



Jean is only supporting full duplex mode on point to point links,
which disallows the use of a hub.

Regards,
Allan.

In newsgroup: comp.arch.fpga


Full-duplex Ethernet is *not* a bus and does *not* use CSMA/CD.  It's
a point-to-point self-clocking serial connection.  All
interconnections have to be done at layer 2 (i.e. by bridges/switches)
or higher.

    -hpa