DATA STRUCTURES AND REGISTERS
reserved for the status word, the next word is
PACKET FORMAT IN BUFFER MEMORY
used to specify the total number of bytes, and it
is followed by the data area. The data area
holds the packet itself.
The packet format in memory is similar for the
Transmit and Receive areas. The first word is
bit 0
bit 15
RAM
OFFSET
(Decimal)
0
STATUS WORD
BYTE COUNT
2
RESERVED
4
DATA AREA
2046 Max
CONTROL BYTE
LAST DATA BYTE (if odd)
FIGURE 4 – DATA PACKET FORMAT
TRANSMIT PACKET
RECEIVE PACKET
STATUS WORD
Written by CSMA upon transmit Written by CSMA upon receive
completion (see Status
Register)
completion (see RX Frame
Status Word)
BYTE COUNT
DATA AREA
Written by CPU
Written by CSMA
Written by CSMA
Written/modified by CPU
CONTROL BYTE
Written by CPU to control
odd/even data bytes
Written by CSMA; also has
odd/even bit
18
SMSC [ SMSC CORPORATION ]
