8101 Datasheet, PDF (25/172 Pages) LSI Computer Systems – Gigabit Ethernet Controller

source address (SA), length/type field (L/T), data, frame check sequence
(FCS), and interpacket gap (IPG). The format for the Ethernet frame is
shown in Figure 2.2.
An Ethernet frame is specified by IEEE 802.3 to have a minimum length
of 64 bytes and a maximum length of 1518 bytes, exclusive of the
preamble and SFD. Packets that are less than 64 bytes or greater than
1518 bytes are referred to as undersize and oversize packets,
respectively.
2.5.1 Preamble and SFD
The preamble and SFD is a combined 64-bit field consisting of 62
alternating ones and zeros followed by a 0b11 end of preamble indicator.
The first 56-bits of ones and zeros are considered to be the preamble,
and the last 8 bits (0b10101011) are considered to be the SFD.
2.5.2 Destination Address
The destination address is a 48-bit field containing the address of the
station(s) to which the frame is directed. The format of the address field
is the same as defined in IEEE 802.3 and shown in Figure 2.2 b. The
destination address can be either a unicast address to a specific station,
a multicast address to a group of stations, or a broadcast address to all
stations. The first and second bits determine whether an address is
unicast, multicast or broadcast, and the remaining 46 bits are the actual
address bits, as shown in Figure 2.2 b.
2.5.3 Source Address
The source address is a 48-bit field containing the specific station
address from which the frame originated. The format of the address field
is the same as defined in IEEE 802.3 and shown in Figure 2.2 b.
2.5.4 Length/Type Field
The 16-bit length/type field takes on the meaning of either packet length
or packet type, depending on its numeric value, as described in
Table 2.1.
Ethernet Frame Format
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