Freescale Semiconductor MPC8260 - Manual (Page 1221)

Fast Ethernet Controller
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
Freescale Semiconductor 35-25
Figure 35-9. Ethernet Receiving Using RxBDs
35.20 Ethernet TxBDs
Data is sent to the Ethernet controller for transmission on an FCC channel by arranging it in buffers
referenced by the channel’s TxBD table. The Ethernet controller uses TxBDs to confirm transmission or
indicate errors so the core knows when buffers have been serviced.
Figure 35-10 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
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
(6)