Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 734

SCC Asynchronous HDLC Mode and IrDA
Bits Name
13 CR Rx CRC error. Set when a frame has a CRC error. Received CRC bytes are written to the buffer.
14 OV Overrun. Set when a receiver overrun occurs during frame reception.
15 CD Carrier detect lost. Set when CD is negated during frame reception.
The data length and buffer pointer fields are described in
Because asynchronous HDLC is a frame-based protocol, RxBD[Data Length] of the last buffer of a frame
contains the total number of frame bytes, including the 2 or 4 bytes for CRC.
25.15 SCC Asynchronous HDLC TxBDs
The CPM uses the TxBD, shown in
0 1
Offset + 0 R —
Offset + 2
Offset + 4
Offset + 6
Table 25-11 describes the SCC asynchronous HDLC TxBD status and control fields.
Bits Name
0 R Ready
0 The buffer is not ready for transmission; the BD and the buffer can be updated. The CPM clears
R after the buffer is sent or after an error condition.
1 The buffer is ready but is not sent or is being sent. Do not update the BD while R =1.
1 — Reserved, should be cleared.
2 W Wrap (last BD in table)
0 Not the last BD in the table
1 The last BD in the table. After this buffer is used, the CPM sends incoming data using the BD
pointed to by TBASE. The number of TxBDs in this table are determined only by the W bit.
3 I Interrupt
0 SCCE[TXB] is not set after this buffer is sent.
1 SCCE[TXB] is set when this buffer is sent by the asynchronous HDLC controller.
4 L Last
0 Not the last buffer in the current frame.
1 Last buffer in the current frame. The proper CRC and closing flag are sent after the last byte.
5 — Reserved, should be cleared.
25-12
Table 25-10. Asynchronous HDLC RxBD Status
and Control Field Descriptions (continued)
Figure 25-8, to confirm transmissions and indicate error conditions.
2 3 4 5 6
W I L — CM
Tx Buffer Pointer
Figure 25-8. SCC Asynchronous HDLC TxBDs
Table 25-11. Asynchronous HDLC TxBD Status
and Control Field Descriptions
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Description
Section 21.3, "SCC Buffer Descriptors (BDs)."
7
—
Data Length
Description
14 15
CT
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