LAN91C111_11 Datasheet, PDF (44/133 Pages) SMSC Corporation – 10/100 Non-PCI Ethernet Single Chip MAC + PHY

10/100 Non-PCI Ethernet Single Chip MAC + PHY
Datasheet
BYTE COUNT - Divided by two, it defines the total number of words including the STATUS WORD,
the BYTE COUNT WORD, the DATA AREA, the CRC, and the CONTROL BYTE. The CRC is not
included if the STRIP_CRC bit is set. The maximum number of bytes in a RAM page is 2048 bytes.
The receive byte count always appears as even; the ODDFRM bit of the receive status word indicates
if the low byte of the last word is relevant.
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 LAN91C111 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 LAN91C111. 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 meaning only 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.
Revision 1.92 (06-27-11)
44
DATASHEET
SMSC LAN91C111 REV C