[ethmac] Ethernet Standard Related queries.

["Mohan Krishna" <mkrishna@tataelxsi.co.in>]

Hi All.,
   Thanks for clarifying my doubt on Preamble & SFD.

   I have  a few questions regarding the ETHERNET standard:

1. Some documents specify the "Destination Address & Source Address " as 2 or 6Octets.What is the
correct length of  D.A & S.A fields?
2. Also the LENGTH/TYPE field is specified as 2octets in some documents and 4 octets in other
document.
    I assume its always 2 octets. Correct me if I am wrong.

Also I would like to know whether the copy available for download in the IEEE website (IEEE Std
802.3-2002® (Revision of IEEE Std 802.3®, 2000 Edition)
is the latest one for reference.

Thanks in Advance.

Regards.
Mohan


Illan Glasner wrote:

> Yes you are tho' keep in mind the the SFD is not 1011 but rather 10101011 as
> many time since in FE we work in nibble boundry it is common to define pre
> as 1010 and sfd as 1011 and in such case you need at least one pre before
> the sfd.
>
> have a nice day
>
>    Illan
>
> -----Original Message-----
> From: Karthik D [mailto:karthikd@myw.ltindia.com]
> Sent: Friday, December 06, 2002 6:14 AM
> To: ethmac@opencores.org
> Cc: mkrishna@tataelxsi.co.in
> Subject: Re: [ethmac] necessity of preamble during reception
>
> ** Proprietary **
> ** High Priority **
>
> "RX_DV (Receive Data Valid) is driven by the PHY to indicate that the PHY is
> presenting recovered and decoded nibbles on the RXD bundle and that the data
> on RXD is synchronous to RX_CLK. RX_DV shall transition synchronously with
> respect to the RX_CLK. RX_DV shall remain asserted continuously from the
> first recovered nibble of the frame through the final recovered nibble and
> shall be negated prior to the first RX_CLK that follows the final nibble. In
> order for a received frame to be correctly interpreted
> by the Reconciliation sublayer and the MAC sublayer, RX_DV must encompass
> the frame, starting no later than the Start Frame Delimiter (SFD) and
> excluding any End-of-Frame delimiter"
>
> This tells that we need to look for valid SFD rather than Preamble to
> receive the frame.
>
> Hope i am correct...
>
> Karthik D.
>
> >>> mkrishna@tataelxsi.co.in 12/06/02 05:45PM >>>
> hi all,
>
> I have simple doubt.During reception of a frame is it required that all
> the preamble(i.e 6 octets) has to be received or is it suffucicient that
> a valid SFD is received before the frame can be processed.
>
> Thanks in advance
> Mohan
>
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