Motorola MPC823e Reference Manual page 794

Communication Processor Module
16.9.23.2 SCCx ETHERNET RECEIVE BUFFER DESCRIPTOR. The SCCx Ethernet
controller uses the receive (RX) buffer descriptor to report information about the received
data for each buffer. Figure 16-109 illustrates an Ethernet receive buffer descriptor example.
RECEIVE BD 0
E L
0
0
STATUS
0040
LENGTH
32-BIT BUFFER POINTER
POINTER
RECEIVE BD 1
E L
0
1
STATUS
0045
LENGTH
32-BIT BUFFER POINTER
POINTER
RECEIVE BD 2
E
STATUS 1
LENGTH
POINTER 32-BIT BUFFER POINTER
RECEIVE BD 3
E
STATUS 1
LENGTH XXXX
POINTER 32-BIT BUFFER POINTER
NON-COLLIDED ETHERNET FRAME 1
TWO FRAMES
RECEIVED IN ETHERNET
TIME
Figure 16-109. Ethernet Receive Buffer Descriptor Example
16-340
F
1
F
0
CLOSED AFTER
RECEIVED.
OPTIONAL TAG
APPENDED
XXXX
COLLISION
CAUSES BUFFER
REUSED
LINE IDLE
MPC823e REFERENCE MANUAL
MRBLR = 64 BYTES FOR THIS SCC
BUFFER
DEST ADDRESS (6)
SOURCE ADDRESS (6)
TYPE/LENGTH (2)
BUFFER
FULL
DATA BYTES (50)
BUFFER
CRC BYTES (4)
TAG BYTE (1)
BUFFER
EMPTY
CRC
BYTE
BUFFER
OLD DATA FROM
COLLIDED FRAME WILL
BE OVERWRITTEN.
EMPTY
TO BE
BUFFER
BUFFER
EMPTY
STILL
EMPTY
FRAME 2
PRESENT
COLLISION
64 BYTES
64 BYTES
64 BYTES
64 BYTES
TIME
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