8101 Datasheet, PDF (36/172 Pages) LSI Computer Systems – Gigabit Ethernet Controller

2.8.3 Unicast Address Filter
Comparing the destination address of the receive packet against the
48-bit value stored in the three MAC Address registers (registers 0, 1
and 2) filters unicast packets. When the destination address of a unicast
packet matches the value stored in these registers the unicast packet is
deemed valid and passed to the receive FIFO; otherwise, the packet is
rejected. The correspondence between the bits in the MAC Address
registers and the incoming bits in the destination address of the receive
packet is defined in the MAC Address register definitions.
To program the controller to always reject unicast packets, set the
REJUCST bit in “Register 8–Configuration 2‚" Section 4.3.9. When this
bit is set all unicast packets are rejected regardless of their address.
Unicast packet address filtering functions do not affect the reception of
MAC control frames. Other bits described in Section 2.17, “MAC Control
Frames,” control the reception of MAC control frames.
2.8.4 Multicast Address Filter
The multicast address filter function computes the CRC on the incoming
Destination Address and produces a 6-bit number that is compared
against the 64 values stored in the MAC Address Filter 1−4 registers
(Registers 3, 4, 5, and 6). When the multicast packet destination address
passes the address filter, the packet is deemed valid and passed to the
receive FIFO; otherwise, the packet is rejected.
The multicast address filter requires 64 address filter bits to be written
into the Address Filter 1−4 registers. The multicast address filtering
algorithm is as follows:
1. Compute a separate 32-bit CRC on the destination address field
using the same IEEE 802.3 defined method that computes the
transmit CRC.
2. Use bits [0:2] of the destination address FCS to select one of the
bytes in the 64-bit address filter, as shown in Table 2.5.
3. Use bits [3:5] of the destination address FCS to select one of the bits
within the byte selected in (2), as shown in Table 2.5.
2-18
Functional Description
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