SMC91C100 Datasheet, PDF (45/83 Pages) List of Unclassifed Manufacturers – FEAST Fast Ethernet Controller

The 64 bit multicast table is used for group
address filtering. The hash value is defined as the
six most significant bits of the CRC of the
destination addresses. The three msb's
determine the register to be used (MT0-7), while
the other three determine the bit within the
register.
If the appropriate bit in the table is set, the packet
is received.
If the ALMUL bit in the RCR register is set, all
multicast addresses are received regardless of the
multicast table values.
Hashing is only a partial group addressing filtering
scheme, but being the hash value available as part
of the receive status word, the receive routine can
reduce the search time significantly. With the
proper memory structure, the search is limited to
comparing only the multicast addresses that have
the actual hash value in question.
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