FEAST Fast Ethernet Controller for PCMCIA and Generic 16-Bit Applications
The transmit byte count least significant bit will be assumed 0 by the controller regardless of the value written in memory.
DATA AREA - The data area starts at offset 4 of the packet structure and can extend up to 2043 bytes.
The data area contains six bytes of DESTINATION ADDRESS followed by six bytes of SOURCE ADDRESS, followed by
a variable-length number of bytes. On transmit, all bytes are provided by the CPU, including the source address. The
LAN91C110 does not insert its own source address. On receive, all bytes are provided by the CSMA side.
The 802.3 Frame Length word (Frame Type in Ethernet) is not interpreted by the LAN91C110. 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 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
HASH VALUE
MULT
CAST
BYTE
5
4
3
2
1
0
ALGNERR - Frame had alignment error. When MII SEL=1 alignment error is set when BADCRC=1 and an odd number of
nibbles was received between SFD and RX_DV going inactive.
BRODCAST - Receive frame was broadcast.
BADCRC - Frame had CRC error, or RX_ER was asserted during reception.
SMSC DS – LAN91C110 REV. B
Page 14
Rev. 09/05/02
SMSC [ SMSC CORPORATION ]
