Motorola MPC8260 User Manual

23-10

MOTOROLA

Data length and buffer pointer Þelds are described in Section 19.2, ÒSCC Buffer
Descriptors (BDs).Ó The Rx buffer pointer must be divisible by four, unless
GSMR_H[RFW] is set to 8 bits wide, in which case the pointer can be even or odd. The
buffer can reside in internal or external memory.

Data is sent to the CPM for transmission on an SCC channel by arranging it in buffers
referenced by the TxBD table. The CPM uses BDs to conÞrm transmission or indicate error
conditions so the processor knows buffers have been serviced. Prepare status and control
bits before transmission; they are set by the CPM after the buffer is sent. 

3

Interrupt. 
0 No interrupt is generated after this buffer is used. 
1 When this buffer is closed by the transparent controller, the SCCE[RXB] is set. SCCE[RXB] can 

cause an interrupt if it is enabled.

4

L

Last in frame. Set by the transparent controller when this buffer is the last in a frame, which occurs 
when CD is negated (if GSMR_H[CDP] = 0) or an error is received. If an error is received, one or more 
of RxBD[OV, CD, DE] are set. Note that the SCC transparent controller writes the number of buffer (not 
frame) octets to the last BDÕs data length Þeld. 
0 Not the last buffer in a frame. 
1 Last buffer in a frame.

5

F

First in frame. The transparent controller sets F when this buffer is the Þrst in the frame:
0 Not the Þrst buffer in a frame.
1 First buffer in a frame.

6

Continuous mode. 
0 Normal operation.
1 The CPM does not clear RxBD[E] after this BD is closed, letting the buffer be overwritten when the 

CPM next accesses this BD. However, RxBD[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 by the transparent controller when a DPLL error occurs as this buffer is received. In 
decoding modes, where a transition is promised every bit, DE is set when a missing transition occurs. 
If a DPLL error occurs, no other error checking is performed.

9Ð10

Ñ

Reserved, should be cleared.

11

NO

Rx non-octet. Set when a frame containing a number of bits not exactly divisible by eight is received.

12

Ñ

Reserved, should be cleared.

13

CR

CRC error indication bits. Indicates that this frame contains a CRC error. The received CRC bytes are 
always written to the receive buffer. CRC checking cannot be disabled, but it can be ignored.

14

OV

Overrun. Indicates that a receiver overrun occurred during buffer reception.

15

CD

Carrier detect lost. Indicates when CD is negated during buffer reception.