Motorola MPC8260 - Manual (Page 900)

30-26 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA
Part IV. Communications Processor Module
Figure 30-9. Ethernet Receiving Using RxBDs
30.20 Ethernet TxBDs
Data is sent to the Ethernet controller for transmission on an FCC channel by arranging it
in buffers referenced by the channelÕs TxBD table. The Ethernet controller uses TxBDs to
conÞrm transmission or indicate errors so the core knows when buffers have been serviced.
Figure 30-10 shows the FCC Ethernet TxBD format.
Buffer
0
0x0040
32-Bit Buffer Pointer
1
E F
Receive BD 0
Status
Length
Pointer
0
0x0045
32-Bit Buffer Pointer
0
E F
Receive BD 1
Status
Length
Pointer
1
XXXX
32-Bit Buffer Pointer
E
Receive BD 2
Status
Length
Pointer
1
XXXX
32-Bit Buffer Pointer
E
Receive BD 3
Status
Length
Pointer
Destination Address (6)
Source Address (6)
Type/Length (2)
Buffer
CRC Bytes (4)
Tag Byte (1)
Buffer
Buffer
Old Data from
Empty
64 Bytes
64 Bytes
64 Bytes
64 Bytes
Two Frames
Received in Ethernet
Collision
Line Idle
Present
Time
Time
Buffer Full
Buffer Closed
after CRC Received.
Buffer
Still Empty
Empty
MRBLR = 64 Bytes for this FCC
Empty
Data Bytes (50)
Optional Tag Byte
Collision
Causes Buffer
to be Reused
0
L
1
L
Frame 2
Collided Frame Will
be Overwritten
Appended
Non-Collided Ethernet Frame 1