Communication between FPGA and PC with ethernet

hello
i am doing a project called "10 BASE T ETHERNET INTERFACE USING FPGA"
i am using a xilinx's spartan2   XC2S50 chip and using VHDL.now i
wanted to ask if any of u have any information on the codes of VHDL
that i'll be needing and related stuff.
if u happen to have any thing at all kindly send them to me. another
question.
  ethernet traffic is digital. now a logic "zero" must be a
band of voltage and similarly a logic "one". now i wanted to ask if i
am
using a 10/100 Mbps ethernet card or lan card as they are called what
will be my voltages level. ie the RJ 45 female of my lan card will send

a logic "0" at which voltage/voltage band  and on what voltage/voltage
band will be logic"1". its important to find these as i am connecting
FPGA to lan card and hoping that signals fm lan card does not blow up
the damn chip.
  your early positive reply will save me lots of time.hope u will be
able to able to spare some time.
thanku all

On 21 Feb 2006 13:20:50 -0800, "aayush" <aayush_v2@rediffmail.com>
wrote:
>  ethernet traffic is digital. 

not if you're looking at the cat3 wire.

> now a logic "zero" must be a
>band of voltage and similarly a logic "one". 
Not really. For 10bt, a {high,low} is one and {low,high} is zero. Read
about Manchaster coding. For 100btx it is quite a bit more
complicated.

> now i wanted to ask if i am
>using a 10/100 Mbps ethernet card or lan card as they are called what
>will be my voltages level. ie the RJ 45 female of my lan card will send
>a logic "0" at which voltage/voltage band  and on what voltage/voltage
>band will be logic"1". its important to find these as i am connecting
>FPGA to lan card and hoping that signals fm lan card does not blow up
>the damn chip.

You always need a network chip (at least a PHY or PHY+MAC) which you
connect to the RJ45 to talk to the wire. You shouldn't connect the
FPGA to the RJ45 directly. If you connect FPGA to the LAN card you
don't need to know anything about what goes on the wire as it
completely isolates it from you and gives you well-behaved bits.

hansp wrote:
> Check out this link for some ideas:
> http://www.fpga4fun.com/10BASE-T.html

Yes, I've built the transmitter twice (in both altera and xilinx) parts
and it more or less worked.  In one case I had to send it through a
switch before an embedded ethernet board could understand it.   Haven't
tried the receiver.  Getting it to do anything usefull is a bit
different though.  BTW you probably need to be local amin on a win XP
box to receive UDP packets...

There are really a bunch of options:

- A serial to ethernet converter module, which may handle a TCP/IP
protocol for you (LANCHIP, etc)

- An ethernet chip or card intended for PC-ISA - lots of embeded guys
have used these (avoid PCI though)

- using an ethernet "PHY" chip to interface to the cable (with
transformer of course) and then implementing the "MAC" function along
with all the protocol stuff in the FPGA

- implementing everything in the FPGA except for the transforer (yes,
some people cheat with capacitor coupling).  This is what the FPGA4FUN
project does.