Ethernet (ETH): media access control (MAC) with DMA controller RM0090
1126/1731 DocID018909 Rev 11
Figure 360 and Figure 361 describe the frame structure (untagged and tagged) that
includes the following fields:
• Preamble: 7-byte field used for synchronization purposes (PLS circuitry)
Hexadecimal value: 55-55-55-55-55-55-55
Bit pattern: 01010101 01010101 01010101 01010101 01010101 01010101 01010101
(right-to-left bit transmission)
• Start frame delimiter (SFD): 1-byte field used to indicate the start of a frame.
Hexadecimal value: D5
Bit pattern: 11010101 (right-to-left bit transmission)
• Destination and Source Address fields: 6-byte fields to indicate the destination and
source station addresses as follows (see Figure 359):
– Each address is 48 bits in length
– The first LSB bit (I/G) in the destination address field is used to indicate an
individual (I/G = 0) or a group address (I/G = 1). A group address could identify
none, one or more, or all the stations connected to the LAN. In the source address
the first bit is reserved and reset to 0.
– The second bit (U/L) distinguishes between locally (U/L = 1) or globally (U/L = 0)
administered addresses. For broadcast addresses this bit is also 1.
– Each byte of each address field must be transmitted least significant bit first.
The address designation is based on the following types:
• Individual address: this is the physical address associated with a particular station on
the network.
• Group address. A multidestination address associated with one or more stations on a
given network. There are two kinds of multicast address:
– Multicast-group address: an address associated with a group of logically related
stations.
– Broadcast address: a distinguished, predefined multicast address (all 1’s in the
destination address field) that always denotes all the stations on a given LAN.
Figure 359. Address field format
• QTag Prefix: 4-byte field inserted between the Source address field and the MAC Client
Length/Type field. This field is an extension of the basic frame (untagged) to obtain the
tagged MAC frame. The untagged MAC frames do not include this field. The
extensions for tagging are as follows:
– 2-byte constant Length/Type field value consistent with the Type interpretation
(greater than 0x0600) equal to the value of the 802.1Q Tag Protocol Type (0x8100
MSB LSB
Bit transmission order (right to left)
U/L
I/G
46-bit address
I/G = 0 Individual address
I/G = 1 Group address
U/L = 0 Globally administered address
U/L = 1 Locally administered address
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