Motorola MPC8260 User Manual
MOTOROLA
Chapter 26. Serial Management Controllers (SMCs)
26-27
Part IV. Communications Processor Module
Data length and buffer pointer Þelds are described in Section 19.2, ÒSCC Buffer
Descriptors (BDs).Ó
Descriptors (BDs).Ó
26.4.9 SMC Transparent TxBD
Data is sent to the CP for transmission on an SMC channel by arranging it in buffers
referenced by the channel TxBD table. The CP uses BDs to conÞrm transmission or
indicate error conditions so the processor knows buffers have been serviced.
referenced by the channel TxBD table. The CP uses BDs to conÞrm transmission or
indicate error conditions so the processor knows buffers have been serviced.
Table 26-15 describes SMC transparent TxBD Þelds.
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Offset + 0
R
Ñ
W
I
L
Ñ
CM
Ñ
UN
Ñ
Offset + 2
Data Length
Offset + 4
Tx Data Buffer Pointer
Offset + 6
Table 26-14. SMC Transparent TxBD
Table 26-15. 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
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 data buffer is not sent or is being sent. BD Þelds cannot 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
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 theW bit
and overall space constraints of the dual-port RAM.
and overall space constraints of the dual-port RAM.
3
I
Interrupt.
0 No interrupt is generated after this buffer is serviced.
1 SMCE[TXB] or SMCE[TXE] are set when the buffer is serviced. They can cause interrupts if they are
0 No interrupt is generated after this buffer is serviced.
1 SMCE[TXB] or SMCE[TXE] are set when the buffer is serviced. They can cause interrupts if they are
enabled.
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
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
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.
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.