byte order of ethernet destination address

Hi people, A simple and may be silly query for you. Can you tell me which byte of the ethernet destination address follows the start frame delimeter(SFD) on the gmii data bus....is it the byte 0(bits 7:0) or byte 6 (bits 47:39)? I think its byte 0 but want to make sure so please let me know. Thanks

Reply to
pranavtailor
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The one on the left when you write the number on paper.

Most likely the one at a lower address when stored in memory, as it will be the lower address in the output buffer.

Some people, and some machine architects, number bytes in a word with 0 on the left, some with 0 on the right. Some are little endian, some big endian.

-- glen

Reply to
glen herrmannsfeldt

If you start with byte 0, you'd end with byte 5, not 6. Minor detail...

You are correct. If you look at a written representation of a MAC address, the bytes are transmitted as you would read them from left to right. For example, if the MAC address was 00:4b:50:12:34:56, then the byte that would come after the SFD would be 00, followed by 4b, etc.

Inside the bytes, the bits are transmitted least-significant-bit first. The very first bit (the low bit of the first byte) is the multicast bit. The second bit is the "Locally Administered" bit. For non-multicast MAC addresses, the following 22 bits indicate the vendor OUI (Organizationally Unique Identifier), and the last 24 bits are assigned arbitrarily by the vendor to provide uniqueness.

Patrick ========= For LAN/WAN Protocol Analysis, check out PacketView Pro! ========= Patrick Klos Email: snipped-for-privacy@klos.com Klos Technologies, Inc. Web:

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Reply to
Patrick Klos

Reply to
pranavtailor

The standards only talk about the transmission order once the data gets on to the transmission media.

If for some reason you built your transmitter to buffer an octet at a time and transmit the octet in reverse order, then for consistancy the GMII data would have to be reversed as well.

There are standards about GBICs and SFP's, so you wouldn't pull a trick like that if you were planning to use a -standard- GBIC or SFP, but it wouldn't be the first time that a manufacturer customized a transmission device to lock people in to their parts.

Reply to
Walter Roberson

The MII for fast ethernet is part of the standard, and I thought GMII was also, though it rarely exists outside of the chips.

In any case, that would be the expected ordering.

-- glen

Reply to
glen herrmannsfeldt

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