91C100FDREVB Datasheet, PDF (17/68 Pages) SMSC Corporation – FEAST FAST ETHERNET CONTROLLER WITH FULL DUPLEX CAPABILITY

The 802.3 Frame Length word (Frame Type in Ethernet) is not interpreted by the LAN91C100FD. It is treated transparently
as data both for transmit and receive operations.
CONTROL BYTE - For transmit packets the CONTROL BYTE is written by the CPU as:
X
X
ODD
CRC
0
0
0
0
ODD - If set, indicates an odd number of bytes, with the last byte being right before the CONTROL BYTE. If clear, the
number of data bytes is even and the byte before the CONTROL BYTE is not transmitted.
CRC - When set, CRC will be appended to the frame. This bit has only meaning if the NOCRC bit in the TCR is set.
For receive packets the CONTROL BYTE is written by the controller as:
0
1
ODD
0
0
0
0
0
ODD - If set, indicates an odd number of bytes, with the last byte being right before the CONTROL BYTE. If clear, the
number of data bytes is even and the byte before the CONTROL BYTE should be ignored.
RECEIVE FRAME STATUS WORDRECEIVE 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
BAD
CRC
ODD
FRM
TOO
TOOLNG _SHORT
LOW
BYTE
HASH VALUE
MULT
CAST
5
4
3
2
1
0
ALGNERR - Frame had alignment error. When MII SEL=1 alignmet error is set when BADCRC=1 and an odd number of
nibbles was 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.
TOOLNG - Frame length was longer than 802.3 maximum size (1518 bytes on the cable).
TOOSHORT - Frame length was shorter than 802.3 minimum size (64 bytes on the cable).
SMSC DS – LAN91C100FD REV. B
Page 17
Rev. 05/31/2000