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DATA LENGTH
This field represents the number of octets that the communication processor module writes
into this buffer descriptor data buffer. The communication processor module writes it once
as the buffer descriptor is closed. The serial peripheral interface writes these bits after the
received data is placed into the associated data buffer. The actual amount of memory
allocated for this buffer must be greater than or equal to the MRBLR entry.
RX DATA BUFFER POINTER
This field always points to the first location of the associated data buffer. It must be even and
it can reside in internal or external memory. The serial peripheral interface writes these bits
after the received data is placed into the associated data buffer.
16.12.4.1.3 SPI Transmit Buffer Descriptor. Data to be transmitted by the serial
peripheral interface is sent to the communication processor module by arranging it in buffers
referenced by the transmit (TX) buffer descriptor ring. The first word of the TX buffer
descriptor contains status and control bits. You must prepare the following bits before
transmitting data.
0
1
2
R
RES
W
OFFSET + 0
OFFSET + 2
OFFSET + 4
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, but you must clear them before submitting the buffer descriptor to the
communication processor module.
R—Ready
0 = The data buffer associated with this buffer descriptor is not ready for transmission
and you are free to manipulate it or its associated data buffer. The communication
processor module clears this bit after the buffer is transmitted or after an error
occurs.
1 = The data buffer, which you prepare for transmission, is not transmitted yet or is
currently being transmitted. You cannot write any fields of this buffer descriptor
once this bit is set.
Bits 1, 5, and 7–13—Reserved
These bits are reserved and must be set to 0.
MOTOROLA
3
4
5
6
7
I
L
RES
CM
DATA LENGTH
TX DATA BUFFER POINTER
MPC823e REFERENCE MANUAL
Communication Processor Module
8
9
10
11
12
13
RESERVED
14
15
UN
ME
16-449
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