91C94 Datasheet, PDF (29/120 Pages) SMSC Corporation – ISA/PCMCIA SINGLE CHIP ETHERNET CONTROLLER WITH RAM

RECEIVE FRAME STATUS WORD
This word is written at the beginning of each receive frame in memory. It is not available as a register.
HIGH
BYTE
ALGN
ERR
BROD
CAST
TOO
BADCRC ODDFRM TOOLNG SHORT
LOW
BYTE
HASH VALUE
MULT
CAST
5
4
3
2
1
0
ALGNERR Frame had alignment error.
BRODCAST Receive frame was broadcast.
BADCRC Frame had CRC error.
ODDFRM This bit when set indicates that the
received frame had an odd number of bytes.
TOOLNG The received frame is longer than the
802.3 maximum size (1518 bytes on the cable).
TOOSHORT The received frame is shorter than
the 802.3 minimum size (64 bytes on the cable).
HASH VALUE Provides the hash value used to
index the Multicast Registers. Can be used by
receive routines to speed up the group address
search. The hash value consists of the six most
significant bits of the CRC calculated on the
Destination Address, and maps into the 64 bit
multicast table. Bits 5,4,3 of the hash value
select a byte of the multicast table, while bits
2,1,0 determine the bit within the byte selected.
Examples of the address mapping:
ADDRESS
ED 00 00 00 00 00
0D 00 00 00 00 00
01 00 00 00 00 00
2F 00 00 00 00 00
HASH VALUE 5-0
000 000
010 000
100 111
111 111
MULTICAST TABLE BIT
MT-0 bit 0
MT-2 bit 0
MT-4 bit 7
MT-7 bit 7
MULTCAST Receive frame was multicast. If
hash value corresponds to a multicast table bit
that is set, and the address was a multicast,
the packet will pass address filtering regardless
of other filtering criteria.
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