Freescale Semiconductor MPC8260 - Manual (Page 802)

SCC Ethernet Mode
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
25-18 Freescale Semiconductor
Figure 25-7. Ethernet Receiving using RxBDs
25.19 SCC Ethernet Transmit Buffer Descriptor
Data is sent to the Ethernet controller for transmission on an SCC channel by arranging it in buffers
referenced by the channel TxBD table. The Ethernet controller uses TxBDs to confirm transmission or
indicate errors so the core knows buffers have been serviced.
Figure 25-8 represents an SCC ethernet
transmit buffer descriptor.
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 SCC
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