26-12
MPC860 PowerQUICC UserÕs Manual
MOTOROLA
Part V. The Communications Processor Module
Table 26-10 describes the SCC asynchronous HDLC RxBD status and control Þelds.
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0
E
Ñ
W
I
L
F
CM
Ñ
BRK BOF
Ñ
AB
CR
OV
CD
2
Data Length
4
Rx Buffer Pointer
6
Figure 26-7. SCC Asynchronous HDLC RxBDs
Table 26-10. Asynchronous HDLC RxBD Status and Control Field Descriptions
Bits
Name
Description
0
E
Empty.
0 The buffer is full or stops receiving because of an error. The core can read or update any Þelds of
this RxBD. The CPM cannot reuse this BD while E = 0.
1 The buffer is not full. The CP controls the BD and buffer. The core should not update the BD.
1
Ñ
Reserved, should be cleared.
2
W
Wrap (last 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 using the BD pointed
to by RBASE. The number of RxBDs in a table is determined by the W bit and overall space
constraints of the dual-port RAM.
3
I
Interrupt.
0 SCCE[RXB] is not set after this buffer is used. SCCE[RXF] is unaffected.
1 SCCE[RXB] or SCCE[RXF] is set when this buffer is used by the asynchronous HDLC controller.
4
L
Last in frame.
0 Not the last buffer in a frame.
1 Set by SCC when a buffer is the last in a frame which happens when a closing ßag or error is
received. If an error occurs, one or more of the BRK, CD, OV, BOF, CR, and AB bits are set. The
SCC updates RxBD[Data Length].
5
F
First in frame. Set by the SCC when this buffer is the Þrst in a frame.
0 Not the Þrst buffer in a frame.
1 First buffer in a frame.
6
CM
Continuous mode.
0 Normal operation.
1 The CP does not clear E after the BD is closed allowing a buffer to be overwritten when the CP next
accesses the BD. However, E is cleared if an error other than CRC occurs during reception,
regardless of CM.
7
Ñ
Reserved, should be cleared.
8
BRK
Break character received. Set when a frame is closed because a break character is received.
9
BOF
Beginning of frame. Set when a frame is closed because a BOF character is received instead of the
expected EOF.
10Ð11 Ñ
Reserved, should be cleared.
12
AB
Rx abort sequence. Set when an abort sequence or framing error terminates a frame.
13
CR
Rx CRC error. Set when a frame has a CRC error. Received CRC bytes are written to the buffer.
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