Motorola MPC823e - Page 794

Communication Processor Module
16-340 MPC823e REFERENCE MANUAL MOTOROLA
SCCs
COMMUNICATION
16
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.
Figure 16-109. Ethernet Receive Buffer Descriptor Example
MRBLR = 64 BYTES FOR THIS SCC
BUFFER
64 BYTES
TIME
BUFFER
BUFFER
BUFFER
FULL
E
LENGTH
RECEIVE BD 0
STATUS
0040
POINTER
0
E
LENGTH
RECEIVE BD 1
STATUS
0045
POINTER
0
1
0
L
E
LENGTH
RECEIVE BD 2
STATUS
POINTER
1
E
LENGTH
RECEIVE BD 3
STATUS
XXXX
POINTER
1
BUFFER
PRESENT
TIME
1
F
0
LF
NON-COLLIDED ETHERNET FRAME 1
TWO FRAMES
RECEIVED IN ETHERNET
LINE IDLE
OLD DATA FROM
COLLIDED FRAME WILL
BE OVERWRITTEN.
CRC BYTES (4)
TAG BYTE (1)
DEST ADDRESS (6)
SOURCE ADDRESS (6)
TYPE/LENGTH (2)
DATA BYTES (50)
COLLISION
32-BIT BUFFER POINTER
32-BIT BUFFER POINTER
32-BIT BUFFER POINTER
32-BIT BUFFER POINTER
FRAME 2
64 BYTES
64 BYTES
64 BYTES
XXXX
BUFFER
CLOSED AFTER
CRC
RECEIVED.
OPTIONAL TAG
BYTE
APPENDED
COLLISION
CAUSES BUFFER
TO BE
REUSED
BUFFER
STILL
EMPTY
EMPTY
EMPTY
EMPTY