SMSC LAN91C111 - Manual (Page 43)

10/100 Non-PCI Ethernet Single Chip MAC + PHY
Datasheet
SMSC LAN91C111 REV C 43 Revision 1.91 (08-18-08)
DATASHEET
Chapter 8 MAC Data Structures and Registers
8.1 Frame Format In Buffer Memory
The frame 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 it is followed by
the data area. The data area holds the frame itself. By default, the last byte in the receive frame format
is followed by the CRC, and the Control byte follows the CRC.
BYTE COUNT - Divided by two, it defines the total number of words including the STATUS WORD,
the BYTE COUNT WORD, the DATA AREA, the CRC, and the CONTROL BYTE. The CRC is not
included if the STRIP_CRC bit is set. The maximum number of bytes in a RAM page is 2048 bytes.
Figure 8.1 Data Frame 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/modified by CPU Written by CSMA
CONTROL BYTE Written by CPU to 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)
0
2
4
2046 Max
CONTROL BYTE
Last Byte
1st Byte 2nd Byte
CRC (4 BYTES)