STM32F101xx, STM32F102xx, STM32F103xx, STM32F105xx and ...

Ethernet (ETH): media access control (MAC) with DMA controller
RM0008
Unicast destination address filter
The MAC supports up to 4 MAC addresses for unicast perfect filtering. If perfect filtering is
selected (HU bit in the Frame filter register is reset), the MAC compares all 48 bits of the
received unicast address with the programmed MAC address for any match. Default
MacAddr0 is always enabled, other addresses MacAddr1–MacAddr3 are selected with an
individual enable bit. Each byte of these other addresses (MacAddr1–MacAddr3) can be
masked during comparison with the corresponding received DA byte by setting the
corresponding Mask Byte Control bit in the register. This helps group address filtering for the
DA. In Hash filtering mode (when HU bit is set), the MAC performs imperfect filtering for
unicast addresses using a 64-bit Hash table. For hash filtering, the MAC uses the 6 upper
CRC bits of the received destination address to index the content of the Hash table. A value
of 000000 selects bit 0 in the selected register, and a value of 111111 selects bit 63 in the
Hash Table register. If the corresponding bit (indicated by the 6-bit CRC) is set to 1, the
unicast frame is said to have passed the Hash filter; otherwise, the frame has failed the
Hash filter.
Multicast destination address filter
The MAC can be programmed to pass all multicast frames by setting the PAM bit in the
Frame filter register. If the PAM bit is reset, the MAC performs the filtering for multicast
addresses based on the HM bit in the Frame filter register. In Perfect filtering mode, the
multicast address is compared with the programmed MAC destination address registers (1–
3). Group address filtering is also supported. In Hash filtering mode, the MAC performs
imperfect filtering using a 64-bit Hash table. For hash filtering, the MAC uses the 6 upper
CRC bits of the received multicast address to index the content of the Hash table. A value of
000000 selects bit 0 in the selected register and a value of 111111 selects bit 63 in the Hash
Table register. If the corresponding bit is set to 1, then the multicast frame is said to have
passed the Hash filter; otherwise, the frame has failed the Hash filter.
Hash or perfect address filter
The DA filter can be configured to pass a frame when its DA matches either the Hash filter
or the Perfect filter by setting the HPF bit in the Frame filter register and setting the
corresponding HU or HM bits. This configuration applies to both unicast and multicast
frames. If the HPF bit is reset, only one of the filters (Hash or Perfect) is applied to the
received frame.
Broadcast address filter
The MAC does not filter any broadcast frames in the default mode. However, if the MAC is
programmed to reject all broadcast frames by setting the BFD bit in the Frame filter register,
any broadcast frames are dropped.
Unicast source address filter
The MAC can also perform perfect filtering based on the source address field of the received
frames. By default, the MAC compares the SA field with the values programmed in the SA
registers. The MAC address registers [1:3] can be configured to contain SA instead of DA
for comparison, by setting bit 30 in the corresponding register. Group filtering with SA is also
supported. The frames that fail the SA filter are dropped by the MAC if the SAF bit in the
Frame filter register is set. Otherwise, the result of the SA filter is given as a status bit in the
Receive Status word (see RDES0: Receive descriptor Word0).
866/995 Doc ID 13902 Rev 9