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Table 31-8 describes the RxBD status and control Þelds.
Table 31-8. SPI RxBD Status and Control Field Descriptions
Bits Name
0
E
Empty.
0 The buffer is full or stopped receiving because of an error. The core can examine or write to any Þelds
of this RxBD, but the CPM does not use this BD while E = 0.
1 The buffer is empty or reception is in progress. The CPM owns this RxBD and its buffer. Once E is set,
the core should not write any Þelds of this RxBD.
1
Ñ
Reserved, should be cleared.
2
W
Wrap (last BD in table).
0 Not the last BD in the RxBD table.
1 Last BD in the RxBD table. After this buffer is used, the CPM receives incoming data using the BD
pointed to by RBASE (top of the table). The number of BDs in this table is determined only by the W
bit and overall space constraints of the dual-port RAM.
3
I
Interrupt.
0 No interrupt is generated after this buffer is Þlled.
1 SPIE[RXB] is set when this buffer is full, indicating the need for the core to process the buffer.
SPIE[RXB] causes an interrupt if not masked.
4
L
Last. Updated by the SPI when the buffer is closed. In slave mode, this occurs because SPISEL was
negated. The SPI updates L after received data is placed in the buffer.
0 This buffer does not contain the last character of the message.
1 This buffer contains the last character of the message.
5
Ñ
Reserved, should be cleared.
6
CM
Continuous mode. Master mode only; in slave mode, CM should be cleared.
0 Normal operation.
1 The CPM does not clear RxBD[E] after this BD is closed; the buffer is overwritten when the CPM next
accesses this BD. This allows continuous reception from an SPI slave into one buffer, which can be
used, for example, for autoscanning of a serial A/D peripheral.
7Ð13 Ñ
Reserved, should be cleared.
14
OV
Overrun. Set when a receiver overrun occurs during reception (slave mode only). The SPI updates OV
after the received data is placed in the buffer.
15
ME
Multimaster error. Set when this buffer is closed because SPISEL was asserted when the SPI was in
master mode. Indicates an arbitration problem between multiple masters on the SPI bus. The SPI
updates ME after the received data is placed in the buffer.
31.7.1.2 SPI Transmit BD (TxBD)
Data to be sent with the SPI is sent to the CPM by arranging it in buffers referenced by
TxBDs in the TxBD table. TxBD Þelds should be prepared before data is sent. The format
of an TxBD is shown in Figure 31-12.
MOTOROLA
Part V. The Communications Processor Module
Description
Chapter 31. Serial Peripheral Interface
31-15
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