30-28
MPC860 PowerQUICC UserÕs Manual
MOTOROLA
Part V. The Communications Processor Module
Table 30-16 describes SMC transparent TxBD Þelds.
Data length represents the number of octets the CP should transmit from this buffer. It is
never modiÞed by the CP. The data length can be even or odd, but if the number of bits in
the transparent character is greater than 8, the data length should be even. For example, to
transmit three transparent 8-bit characters, the data length Þeld should be initialized to 3.
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0
R
Ñ
W
I
L
Ñ
CM
Ñ
UN
Ñ
2
Data Length
4
Tx Buffer Pointer
6
Figure 30-14. SMC Transparent Transmit BD (TxBD)
Table 30-16. SMC Transparent TxBD Field Descriptions
Bits
Name
Description
0
R
Ready.
0 The buffer is not ready for transmission. The BD and buffer can be updated. The CP clears R after
the buffer is sent or after an error occurs.
1 The user-prepared buffer is not sent or is being sent. BD Þelds must not be updated if R is set.
1
Ñ
Reserved, should be cleared.
2
W
Wrap (Þnal BD in 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 programmable and determined 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 unless an error occurs.
1 SMCE[TX] or SMCE[TXE] are set when the buffer is serviced. They can cause interrupts if they are
enabled.
Note that this bit does not mask SMCE[TXE].
4
L
Last in message.
0 The last byte in the buffer is not the last byte in the transmitted transparent frame. Data from the next
transmit buffer (if ready) is sent immediately after the last byte of this buffer.
1 The last byte in this buffer is the last byte in the transmitted transparent frame. After this buffer is
sent, the transmitter requires synchronization before the next buffer is sent.
5
Ñ
Reserved, should be cleared.
6
CM
Continuous mode.
0 Normal operation.
1 The CP does not clear R after this BD is closed, allowing the buffer to be automatically resent when
the CP accesses this BD again. However, the R bit is cleared if an error occurs during transmission,
regardless of how CM is set.
7Ð13
Ñ
Reserved, should be cleared.
14
UM
Underrun. Set when the SMC encounters a transmitter underrun condition while sending the buffer.
15
Ñ
Reserved, should be cleared.
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