lan91c100 Standard Microsystems Corp., lan91c100 Datasheet - Page 20

• Manufacturer Part Number: lan91c100
• Description: Feast ? Ast Ethernet Controller
• Manufacturer: Standard Microsystems Corp.

RECEIVE FRAME STATUS WORD
This word is written at the beginning of each receive frame in memory. It is not available as a register.
ALGNERR Frame had alignment error. When
MII SEL=1 alignment error is set when
BADCRC=1 and an odd number of nibbles were
received between SFD and RX_DV going
inactive. When MII SEL=0 alignment error is set
when BADCRC=1 and the number of bits
received between SFD and the CRS going
inactive is not an octet multiple.
BRODCAST Receive frame was broadcast.
BADCRC Frame had CRC error, or RX_ER was
asserted during reception.
ODDFRM This bit, when set, indicates that the
received frame had an odd number of bytes.
MULTCAST Receive frame was multicast. If
hash value corresponds to a multicast table bit
that is set, and the address was a multicast,
BYTE
BYTE
HIGH
LOW
ALGN
ERR
ED 00 00 00 00 00
0D 00 00 00 00 00
01 00 00 00 00 00
2f 00 00 00 00 00
ADDRESS
BROD
CAST
5
CRC
BAD
4
HASH VALUE 5-0
000 000
010 000
100 111
111 111
ODD
FRM
20
HASH VALUE
3
TOOLNG Frame length was longer than 802.3
maximum size (1518 bytes on the cable).
TOOSHORT
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.
select a byte of the multicast table, while bits
2,1,0 determine the bit within the byte selected.
Examples of the address mapping:
the packet will pass address filtering regardless
of other filtering criteria.
TOOLNG
MULTICAST TABLE BIT
2
MT-0 bit 0
MT-2 bit 0
MT-4 bit 7
MT-7 bit 7
Frame length was shorter than
SHORT
TOO
Bits 5,4,3 of the hash value
1
0
MULT
CAST