Motorola MPC8260 User Manual
Page 663
MOTOROLA
Chapter 23. SCC Transparent Mode
23-11
Part IV. Communications Processor Module
Table 23-8 describes SCC Transparent TxBD status and control Þelds.
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Offset + 0
R
Ñ
W
I
L
TC
CM
Ñ
UN
CT
Offset + 2
Data Length
Offset + 4
Tx Buffer Pointer
Offset + 6
Figure 23-3. SCC Transparent Transmit Buffer Descriptor (TxBD)
Table 23-8. SCC Transparent TxBD Status and Control Field Descriptions
Bit
Name
Description
0
R
Ready.
0 The buffer is not ready for transmission. The BD and buffer can be updated. The CPM clears R after
the buffer is sent or after an error is encountered.
1 The user-prepared buffer is not sent yet or is being sent. This BD cannot be updated while R = 1.
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 CPM receives incoming data into the Þrst BD that
TBASE points to. The number of TxBDs in this table is determined only by TxBD[W] and overall
space constraints of the dual-port RAM.
3
I
Interrupt. Note that clearing this bit does not disable all SCCE[TXE] events.
0 No interrupt is generated after this buffer is serviced.
1 When the CPM services this buffer, SCCE[TXB] or SCCE[TXE] is set. These bits 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 transmit buffer is sent immediately after the last byte of this buffer.
1 The last byte in the 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
TC
Transmit CRC.
0 No CRC sequence is sent after this buffer.
1 A frame check sequence deÞned by GSMR_H[TCRC] is sent after the last byte of this buffer.
6
CM
Continuous mode.
0 Normal operation.
1 The CPM does not clear TxBD[R] after this BD is closed, so the buffer is automatically resent when
the CPM accesses this BD next. However, TxBD[R] is cleared if an error occurs during
transmission, regardless of how CM is set.
7Р13
С
Reserved, should be cleared.
14
UN
Underrun. Set when the SCC encounters a transmitter underrun condition while sending the buffer.
15
CT
CTS lost. Indicates the CTS was lost during frame transmission.