LAN91C94 datasheet(28/120 Pages) SMSC

28 / 120 page

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

even,

the

ODDFRM

bit

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

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.

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.

ODD

CRC

ODD

LAN91C94 Datasheet(PDF) 28 Page - SMSC Corporation

LAN91C94 Datasheet(HTML) 28 Page - SMSC Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL