SMC Networks SMC91C95 - Manual (Page 29)

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PACKET FORMAT IN BUFFER MEMORY
The packet format in memory is similar for the
TRANSMIT and RECEIVE areas. The first
word is 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 8 - DATA PACKET FORMAT
TRANSMIT PACKET RECEIVE PACKET
STATUS WORD Written by CSMA upon transmit
completion (see Status
Register). Written by CSMA upon receive
completion (see RX Frame
Status Word).
BYTE COUNT Written by CPU. Written by CSMA.
DATA AREA Written by CPU. Written by CSMA.
CONTROL BYTE Written by CPU to control
ODD/EVEN data bytes. Written by CSMA. Also has
ODD/EVEN bit.
R E S E R V E D BYTE COUNT (always even)
S TAT U S W O R D
DATA A R E A
L A S T D ATA BYTE (if odd)
bit0 bit15
R A M
O F F S E T
(DECIMAL)
0
2
4
1 5 3 6 M a x
C O N T R O L B Y T E