Mac 802.3 Frame Format - ST STM32F207 Series Reference Manual

Ethernet (ETH): media access control (MAC) with DMA controller
The MAC sublayer performs the following functions associated with a data link control
procedure:
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Data encapsulation (transmit and receive)
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Media access management
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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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28.5.1

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 323
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)
• 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)
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Destination and Source Address fields: 6-byte fields to indicate the destination and
source station addresses as follows (see
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850/1381
Framing (frame boundary delimitation, frame synchronization)
Addressing (handling of source and destination addresses)
Error detection
Medium allocation (collision avoidance)
Contention resolution (collision handling)
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 324 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
Figure 322):
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