91C94 datasheet(27/120 Pages) SMSC

27 / 120 page

PACKET FORMAT IN BUFFER MEMORY

The packet format in memory is similar for the

TRANSMIT and RECEIVE areas. The first word

reserved

for

the status word, the next

word is used to specify the total number of

bytes, and that in turn is followed by the data

area. The data area holds the packet itself, and

its length is determined by the byte count. The

packet memory format is word oriented.

FIGURE 9 – DATA PACKET FORMAT

TRANSMIT PACKET

RECEIVE PACKET

STATUS WORD

Written by CSMA upon transmit

completion

(see

Status

Written by CSMA upon receive

completion

(see

Frame

Status Word).

BYTE COUNT

Written by CPU.

Written by CSMA.

DATA AREA

Written/modified by CPU.

Written by CSMA.

CONTROL BYTE

Written

CPU

control

ODD/EVEN data bytes.

Written by CSMA.

Also has

ODD/EVEN bit.

RESERVED

BYTE COUNT (always even)

STATUS WORD

DATA AREA

LAST DATA BYTE (if odd)

bit0

bit15

RAM

OFFSET

(DECIMAL)

2046 Max

CONTROL BYTE

91C94 Datasheet(PDF) 27 Page - SMSC Corporation

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