Figure 322. Address Field Format - ST STM32F207 Series Reference Manual

RM0033
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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:
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–
•
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:
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–
•
MAC client length/type: 2-byte field with different meaning (mutually exclusive),
depending on its value:
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–
Regardless of the interpretation of the length/type field, if the length of the data field is
less than the minimum required for proper operation of the protocol, a PAD field is
Ethernet (ETH): media access control (MAC) with DMA controller
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.
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 322. Address field format

MSB 46-bit address
Bit transmission order (right to left)
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
hexadecimal). This constant field is used to distinguish tagged and untagged MAC
frames.
2-byte field containing the Tag control information field subdivided as follows: a 3-
bit user priority, a canonical format indicator (CFI) bit and a 12-bit VLAN Identifier.
The length of the tagged MAC frame is extended by 4 bytes by the QTag Prefix.
If the value is less than or equal to maxValidFrame (0d1500) then this field
indicates the number of MAC client data bytes contained in the subsequent data
field of the 802.3 frame (length interpretation).
If the value is greater than or equal to MinTypeValue (0d1536 decimal, 0x0600)
then this field indicates the nature of the MAC client protocol (Type interpretation)
related to the Ethernet frame.
U/L I/G LSB
RM0033 Rev 9
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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