23-18
MPC860 PowerQUICC UserÕs Manual
MOTOROLA
Part V. The Communications Processor Module
Section 22.2, ÒSCC Buffer Descriptors (BDs),Ó describes the data length and buffer pointer
Þelds.
23.18 SCC UART Transmit Buffer Descriptor (TxBD)
The CPM uses BDs to conÞrm transmission and indicate error conditions so the core knows
that buffers have been serviced. Figure 23-9 shows the SCC UART TxBD.
Table 23-11 describes TxBD status and control Þelds.
10
BR
Break received. Set when a break sequence is received as data is being received into this buffer.
11
FR
Framing error. Set when a character with a framing error (a character without a stop bit) is received and
located in the last byte of this buffer. A new Rx buffer is used to receive subsequent data.
12
PR
Parity error. Set when a character with a parity error is received and located in the last byte of this buffer.
A new Rx buffer is used to receive subsequent data.
13
Ñ
Reserved, should be cleared.
14
OV
Overrun. Set when a receiver overrun occurs during reception.
15
CD
Carrier detect lost. Set when the carrier detect signal is negated during reception.
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0
R
Ñ
W
I
CR
A
CM
P
NS
Ñ
CT
2
Data Length
4
Tx Buffer Pointer
6
Figure 23-9. SCC UART Transmit Buffer Descriptor (TxBD)
Table 23-11. SCC UART TxBD Status and Control Field Descriptions
Bit
Name
Description
0
R
Ready.
0 The buffer is not ready. This BD and buffer can be modiÞed. The CPM automatically clears R after
the buffer is sent or an error occurs.
1 The user-prepared buffer is waiting to begin transmission or is being transmitted. Do not modify the
BD once R is set.
1
Ñ
Reserved, should be cleared.
2
W
Wrap (last buffer descriptor in TxBD table).
0 Not the last BD in the table.
1 Last BD in the table. After this buffer is used, the CPM sends data using the BD pointed to by
TBASE. The number of TxBDs in this table is determined only by the W bit and space constraints of
the dual-port RAM.
Table 23-10. SCC UART RxBD Status and Control Field Descriptions (Continued)
Bits Name
Description
Summary of Contents for MPC860 PowerQUICC
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Page 325: ...MOTOROLA Part IV Hardware Interface IV v Part IV Hardware Interface ...
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