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Communication Processor Module
MOTOROLA
MPC823 USER’S MANUAL
16-439
SPI
COMMUNICATION
16
PROCESSOR
MODULE
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 should be greater than or equal to the MRBLR.
RX DATA BUFFER POINTER
This field always points to the first location of the associated data buffer, must be even, and
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 with 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 should prepare the following bits before
transmitting data.
R—Ready
0 = The data buffer associated with this buffer descriptor is not ready for transmission
and you are free to manipulate this buffer descriptor 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.
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
OFFSET + 0
R
RES
WI
L
RES
CM
RESERVED
UN
ME
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.