Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 844

Serial Peripheral Interface (SPI)
Table 30-8. SPI RxBD Status and Control Field Descriptions (continued)
Bits Name
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.
3 I Interrupt
0 No interrupt is generated after this buffer is filled.
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 — 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.
7–13 — 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.
30.7.1.2 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 fields should be prepared before data is sent. The format of an TxBD is shown in
Figure 30-12.
0 1
Offset + 0 R —
Offset + 2
Offset + 4
Offset + 6
30-14
2 3 4 5 6
W I L — CM
Tx Buffer Pointer
Figure 30-12. SPI Transmit BD (TxBD)
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Description
7
—
Data Length
13 14 15
UN ME
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