Scc Bisync Receive Bd (Rxbd) - Freescale Semiconductor MPC850 User Manual

SCC BISYNC Receive BD (RxBD)

26.12 SCC BISYNC Receive BD (RxBD)
The CP uses BDs to report on each buffer received. It closes the buffer, generates a
maskable interrupt, and starts receiving data into the next buffer after any of the following:
• A user-defined control character is received.
• An error is detected.
• A full receive buffer is detected.
• The
ENTER HUNT MODE
• The
CLOSE RX BD
Figure 26-6 shows the SCC BISYNC RxBD.
0 1
E
Offset + 0 —
Offset + 2
Offset + 4
Offset + 6
Table 26-11 describes SCC BISYNC RxBD status and control fields.
Table 26-11. SCC BISYNC RxBD Status and Control Field Descriptions
Bits Name
E
0 Empty.
0 The buffer is full or stopped receiving because of an error. The core can read or write any fields of
this RxBD. The CP does not use this BD as long as the E bit is zero.
1 The buffer is not full. The CP controls this BD and buffer. The core should not update this BD.
1 — Reserved, should be cleared.
W
2 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 first 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.
I
3 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 field.
0 Not the first buffer in the frame.
1 The first buffer in the frame.
5 F First in frame. Set when this is the first buffer in a frame.
0 Not the first buffer in a frame.
1 First buffer in a frame
command is issued.
command is issued.
2 3 4 5
W I CM
L F
Rx Data Buffer Pointer
Figure 26-6. SCC BISYNC RxBD
MPC850 Family User's Manual
6 7 8 9 10
— DE —
Data Length
Description
11 12 13 14
NO PR CR OV
15
CD