Motorola MPC860 PowerQUICC User Manual page 842

Part V. The Communications Processor Module
0 1
Offset + 0 R Ñ
Offset + 2
Offset + 4
Offset + 6
Table 31-9 describes the TxBD status and control Þelds.
Table 31-9. SPI TxBD Status and Control Field Descriptions
Bits Name
0 R Ready.
0 The buffer is not ready to be sent. This BD or its buffer can be modiÞed. The CPM clears R (unless
RxBD[CM] is set) after the buffer is sent (unless RxBD[CM] is set) or an error occurs.
1 The buffer is ready for transmission or is being sent. The BD cannot be modiÞed once R is set.
1 Ñ Reserved, should be cleared.
2 W Wrap (last BD in TxBD table).
0 Not the last BD in the table.
1 Last BD in the table. After this buffer is used, the CPM receives incoming data using the BD pointed
to by TBASE (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 processed if an error does not occur.
1 SPIE[TXB] or SPIE[TXE] are set when this buffer is processed and causes interrupts if not masked.
Note that this bit does not mask SPIE[TXE].
4 L Last.
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. Valid only when the SPI is in master mode. In slave mode, it should be cleared.
0 Normal operation.
1 The CPM does not clear TxBD[R] after this BD is closed, allowing the buffer to be resent
automatically when the CPM next accesses this BD.
7Ð13 Ñ Reserved, should be cleared.
14 UN Underrun. Indicates that the SPI encountered a transmitter underrun condition while sending the buffer.
This error occurs only when the SPI is in slave mode. The SPI updates UN after it sends the buffer.
15 ME Multimaster error. Indicates that this buffer is closed because SPISEL was asserted when the SPI was
in master mode. An arbitration problem occurred between devices on the SPI bus. The SPI updates ME
after sending the buffer.
31-16
2 3 4 5
W I L Ñ CM
Figure 31-12. SPI Transmit BD (TxBD)
MPC860 PowerQUICC UserÕs Manual
6 7 8 9 10
Ñ
Data Length
Tx Buffer Pointer
Description
11 12 13 14 15
UN ME
MOTOROLA