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AT32F435/437
Series Reference Manual
2022.11.11
Page 583
Rev 2.03
26.2.2 EMAC frame communication
Frame format
Figure 26-9 shows the MAC frame format and tagged MAC frame format (Refer to IEEE 802.C-2002
for more information on MAC frame formats)
Figure 26-9 MAC fram e format
Preamble
SFD
DA
SA
MAC client length/type
MAC client data
PAD
FCS
7bytes
1byte
6bytes
6bytes
2bytes
46-1500bytes
4bytes
Figure 26-10 Tagged MAC fram e form at
Preamble
SFD
DA
SA
MAC client length/type
MAC client data
PAD
FCS
7bytes
1byte
6bytes
6bytes
2bytes
46-1500bytes
4bytes
802.1QTag Type
Flag control information
Qtag Prefix 4
bytes
EMAC frame filtering
EMAC supports source and destination address filtering.
Address filtering
Based on frame filtering register chosen by the application, address filtering checks the source and
destination addresses over all received frames using the MAC address and multicast HASH table. The
address filtering status is reported accordingly.
Unicast destination address filter
There are two filtering modes: perfect address filtering and HASH table filtering.
1.
Perfect address filtering: It is enabled by setting HUC=0 in the frame filtering register. Four MAC
addresses are used for perfect filtering. The MACADDR0 is always enabled. The MACADDR1,
MACADDR2 and MACADDR3 bits are enabled using their respective AE bit. The MBC bit in the
address register is set to mask the address comparison of the corresponding bytes. If the MBC bit
is all 0, the EMAC will compare all 48 bits of the received unicast address with the programmed
MAC address, if matched, the unicast address is said to have passed through the filtering.
2.
HASH table filtering: The HUC must be set in the frame filtering register. The EMAC performs
imperfect filtering for unicast addresses through 64-bit HASH table. For HASH filtering, the MAC
calculates the CRC value of the received destination address (see the note below) and uses the 6