
Communication Processor Module
MOTOROLA
MPC823 USER’S MANUAL
16-437
SPI
COMMUNICATION
16
PROCESSOR
MODULE
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 should configure the RX buffer descriptor bits before the serial peripheral
interface is enabled.
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 it 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
should not write any fields of this RX buffer descriptor.
Bit 1, 5, and 7–13—Reserved
These bits are reserved and should be set to 0.
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
OFFSET + 0
E
RES
WI
L
RES
CM
RESERVED
OV
ME
OFFSET + 2
DATA LENGTH
OFFSET + 4
RX 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.