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Table 22-11. SCC BISYNC RxBD Status and Control Field Descriptions (Continued)
Bits Name
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 CP receives incoming data into the Þrst BD that
RBASE points to. The number of BDs in this table is determined by the W bit and by overall space
constraints of the dual-port RAM.
3
I
Interrupt.
0 No interrupt is generated after this buffer is used.
1 SCCE[RXB] is set when the controller closes this buffer, which can cause an interrupt if it is enabled.
4
L
Last in frame. Set when this buffer is the last in a frame. If CD is negated in envelope mode or an error
is received, one or more of the OV, CD, and DE bits are set. The controller writes the number of frame
octets to the data length Þeld.
0 Not the Þrst buffer in the frame.
1 The Þrst buffer in the frame.
5
F
First in frame. Set when this is the Þrst buffer 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 this BD is closed; the buffer is overwritten when the CP accesses this
BD next. However, E is cleared if an error occurs during reception, regardless of how CM is set.
7
Ñ
Reserved, should be cleared.
8
DE
DPLL error. Set when a DPLL error occurs during reception. In decoding modes where a transition is
should occur every bit, the DPLL error is set when a transition is missing.
9Ð10 Ñ
Reserved, should be cleared.
11
NO
Rx non-octet-aligned frame. Set when a frame is received containing a number of bits not evenly
divisible by eight.
12
PR
Parity error. Set when a character with parity error is received. Upon a parity error, the buffer is closed;
thus, the corrupted character is the last byte of the buffer. A new Rx buffer receives subsequent data.
13
CR
Rx CRC error. Set when this frame contains a CRC error. Received CRC bytes are always written to
the receive buffer.
14
OV
Overrun. Set when a receiver overrun occurs during frame reception.
15
CD
Carrier detect lost. Indicates when the carrier detect signal, CD, is negated during frame reception.
Data length and buffer pointer Þelds are described in Section 19.2, ÒSCC Buffer
Descriptors (BDs).Ó Data length represents the number of octets the CP writes into this
buffer, including the BCS. For BISYNC mode, clear these bits. It is incremented each time
a received character is written to the buffer.
MOTOROLA
Part IV. Communications Processor Module
Description
Chapter 22. SCC BISYNC Mode
22-13
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