91C94 Datasheet, PDF (62/120 Pages) SMSC Corporation – ISA/PCMCIA SINGLE CHIP ETHERNET CONTROLLER WITH RAM

HIGH
BYTE
MULTICAST TABLE 7
0
0
0
0
0
0
0
0
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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