参数资料
型号: 91C94
厂商: SMSC Corporation
英文描述: ISA/PCMCIA SINGLE CHIP ETHERNET CONTROLLER WITH RAM
中文描述: 的ISA / PCMCIA的单芯片以太网控制器与RAM
文件页数: 42/120页
文件大小: 447K
代理商: 91C94
28
BYTE COUNT - Divided by two, it defines the
total number of words, including the STATUS
WORD, the BYTE COUNT WORD, the DATA
AREA and the CONTROL BYTE. 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 it can extend for 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 LAN91C94
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 LAN91C94. It
is treated transparently as data for both transmit
and receive operations.
CONTROL BYTE
The CONTROL BYTE always resides on the
high byte of the last word. For transmit packets
the CONTROL BYTE is written by the CPU as:
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:
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.
X
ODD
CRC
0
1
ODD
0
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