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16.12.4.1.2 SPI Receive Buffer Descriptor. Using receive (RX) buffer descriptors, the
communication processor module reports information about each buffer of received data,
closes the current buffer, generates a maskable interrupt, and starts receiving data in the
next buffer once the current buffer is full. Additionally, it closes the buffer when the serial
peripheral interface is configured as a slave and the SPISEL pin goes inactive, thus
indicating that the reception process has stopped.
The first word of the RX buffer descriptor contains status and control bits that you prepare
before reception and then the communication processor module sets them after the buffer
is closed. The second word contains the data length (in bytes) that is received and the third
and fourth words contain a pointer that always points to the beginning of the received data
buffer. You must configure the RX buffer descriptor bits before the serial peripheral interface
is enabled.
0
1
2
OFFSET + 0
E
RES
W
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.
E—Empty
0 = The data buffer associated with this RX buffer descriptor is filled with data or stops
receiving data because an error occurred. The core is free to examine or write to
any fields of this RX buffer descriptor, but the communication processor module
does not use this buffer descriptor as long as the E bit is zero.
1 = The data buffer associated with this buffer descriptor is empty or is currently
receiving data. This RX buffer descriptor and its associated receive buffer are
owned by the communication processor module. Once the E bit is set, the core
must not write any fields of this RX buffer descriptor.
Bit 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
RX DATA BUFFER POINTER
MPC823e REFERENCE MANUAL
Communication Processor Module
8
9
10
11
12
13
RESERVED
14
15
OV
ME
16-447
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