4.2.5. Order of Ethernet Transmission
The TX MAC transmits bytes on the Ethernet link starting with the preamble and ending with the FCS in accordance with the IEEE 802.3 standard. On the transmit client interface, the IP core expects the client to send the most significant bytes of the frame first, and to send each byte in big-endian format. Similarly, on the receive client interface, the IP core sends the client the most significant bytes of the frame first, and orders each byte in big-endian format.
The figure below describes the byte order on the Avalon® streaming interface when the preamble pass-through feature is turned off. Destination Address is the broadcast/multicast bit (a type bit), and Destination Address is a locally administered address bit.
For example, the destination MAC address includes the following six octets AC-DE-48-00-00-80. The first octet transmitted (octet 0 of the MAC address described in the 802.3 standard) is AC and the last octet transmitted (octet 7 of the MAC address) is 80. The first bit transmitted is the low-order bit of AC, a zero. The last bit transmitted is the high order bit of 80, a one.
The preceding table and the following figure show that in this example, 0xAC is driven on DA5 (DA[47:40]) and 0x80 is driven on DA0 (DA[7:0]).
Destination Address is the broadcast/multicast bit (a type bit), and Destination Address is a locally administered address bit.
The destination address and source address bytes follow the preamble pass-through in the same order as in the case without preamble pass-through.