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0
1
Offset + 0
R
Ñ
Offset + 2
Offset + 4
Offset + 6
Table 30-9 describes SMC UART TxBD status and control Þelds.
Table 30-9. SMC UART TxBD Status and Control Field Descriptions
Bits Name
0
R
Ready
0 The buffer is not ready for transmission; BD and its buffer can be altered. The CP clears R after the
buffer has been sent or an error occurs.
1 The buffer has not been completely sent. This BD must not be updated while R is set.
1
Ñ
Reserved, should be cleared.
2
W
Wrap (Þnal BD in the TxBD table)
0 Not the last BD in the table.
1 Last BD in the table. After this buffer is used, the CP receives incoming data into the Þrst BD that
TBASE points to. The number of TxBDs 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 serviced.
1 The SMCE[TX] is set when this buffer is serviced. TX can cause an interrupt if it is enabled.
4Ð5
Ñ
Reserved, should be cleared.
6
CM
Continuous mode
0 Normal operation.
1 The CP does not clear R after this BD is closed and automatically retransmits the buffer when it
accesses this BD next.
7
P
Preamble
0 No preamble sequence is sent.
1 The UART sends one all-ones character before it sends the data so that the other end detects an
idle line before the data is received. If this bit is set and the data length of this BD is zero, only a
preamble is sent.
8Ð15 Ñ
Reserved, should be cleared.
Data length represents the number of octets that the CP should transmit from this BDÕs
buffer. It is never modiÞed by the CP and normally is greater than zero. It can be zero if P
is set, in which case only a preamble is sent. If there are more than 8 bits in the UART
character, data length should be even. For example, to transmit three UART characters of
8-bit data, 1 start, and 1 stop, initialize the data length Þeld to 3. To send three UART
characters of 9-bit data, 1 start, and 1 stop, the data length Þeld should 6, because the three
9-bit data Þelds occupy three half words in memory (the 9 LSBs of each half word).
MOTOROLA
2
3
4
5
W
I
Ñ
CM
Figure 30-8. SMC UART Transmit BD (TxBD)
Chapter 30. Serial Management Controllers
Part V. The Communications Processor Module
6
7
8
9
10
P
Data Length
Tx Buffer Pointer
Description
11
12
13
14
15
Ñ
30-17
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