Mac 802.3 Frame Format - ST STM32F40 Series Reference Manual

Ethernet (ETH): media access control (MAC) with DMA controller
Basically there are two operating modes of the MAC sublayer:
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Half-duplex mode: the stations contend for the use of the physical medium, using the
CSMA/CD algorithms.
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Full duplex mode: simultaneous transmission and reception without contention
resolution (CSMA/CD algorithm are unnecessary) when all the following conditions are
met:
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29.5.1

MAC 802.3 frame format

The MAC block implements the MAC sublayer and the optional MAC control sublayer
(10/100 Mbit/s) as specified by the IEEE 802.3-2002 standard.
Two frame formats are specified for data communication systems using the CSMA/CD MAC:
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Basic MAC frame format
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Tagged MAC frame format (extension of the basic MAC frame format)
Figure 331
includes the following fields:
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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)
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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
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The address designation is based on the following types:
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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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915/1422
physical medium capability to support simultaneous transmission and reception
exactly 2 stations connected to the LAN
both stations configured for full-duplex operation
and Figure 332 describe the frame structure (untagged and tagged) that
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.
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.
Doc ID 018909 Rev 4
Figure 330):
RM0090