
Communication Processor Module
MOTOROLA
MPC823 USER’S MANUAL
16-241
SCC2
COMMUNICATION
16
PROCESSOR
MODULE
Data Length
These bits represent the number of octets the communication processor module writes into
this buffer descriptor data buffer. It is written by the communication processor module once
the buffer descriptor is closed. When this buffer descriptor is the last buffer descriptor in the
frame (L = 1), the data length contains the total number of frame octets, including 2 or 4
bytes for CRC. The actual amount of memory allocated for this buffer should be greater than
or equal to the MRBLR.
RX Data Buffer Pointer
These bits always point to the first location of the associated data buffer, they reside in
internal or external memory, and must be divisible by four.
16.9.16.10 SCC2 HDLC TRANSMIT BUFFER DESCRIPTOR.Data is sent to the SCC2
HDLC controller for transmission on an SCC2 channel by arranging it in buffers referenced
by the channel’s TX buffer descriptor table. Using the transmit (TX) buffer descriptors, the
communication processor module confirms transmission and indicates error conditions so
that the core knows the buffers have been serviced.
R—Ready
0 = The data buffer associated with this buffer descriptor is not ready for transmission.
You are free to manipulate this buffer descriptor or its associated data buffer. The
communication processor module clears this bit after the buffer has been
transmitted or an error condition is encountered.
1 = The data buffer, which you have prepared, has not been transmitted or is currently
being transmitted. You cannot write any fields of this buffer descriptor once this bit
is set.
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
OFFSET + 0
R
RES
WI
L
TC
CM
RESERVED
UN
CT
OFFSET + 2
DATA LENGTH
OFFSET + 4
TX DATA BUFFER POINTER
OFFSET + 6
NOTE:
You are only responsible for initializing the items in bold.
Note:
The communication processor module sets all the status bits in this buffer
descriptor. You should clear all the status bits before submitting the buffer
descriptor to the communication processor module. For example, the parity error
bit is only set when a parity error occurs.