Serial Communication Controllers (SCCs)
7-230
MC68360 USER’S MANUAL
CR—CRC Error indication bits
This frame contains a CRC error. The received CRC bytes are always written to the re-
ceive buffer.
OV—Overrun
A receiver overrun occurred during buffer reception.
CD—Carrier Detect Lost
The carrier detect signal was negated during buffer reception.
Data Length
The data length is the number of octets that the CP has written into this BD’s data buffer.
It is written only once by the CP as the buffer is closed.
NOTE
The actual amount of memory allocated for this buffer should be
greater than or equal to the contents of the maximum receive
buffer length register (MRBLR).
Rx Buffer Pointer
The receive buffer pointer, which always points to the first location of the associated data
buffer, must be divisible by 4 (unless the RFW bit in the GSMR is set to 8-bits wide, in
which case it may be even or odd). The buffer may reside in either internal or external
memory.
7.10.21.10 TRANSPARENT TRANSMIT BUFFER DESCRIPTOR (TX BD). Data is pre-
sented to the CP for transmission on an SCC channel by arranging it in buffers referenced
by the channel’s Tx BD table. The CP confirms transmission or indicates error conditions
using the BDs to inform the processor that the buffers have been serviced.
The status and control bits are prepared by the user before transmission and are set by the
CP after the buffer has been transmitted.
NOTE: Entries in boldface must be initialized by the user.
R—Ready
0 = The data buffer associated with this BD is not ready for transmission. The user is
free to manipulate this BD or its associated data buffer. The CP clears this bit after
the buffer has been transmitted or after an error condition is encountered.
1 = The data buffer, which has been prepared for transmission by the user, has not
been transmitted or is currently being transmitted. No fields of this BD may be writ-
ten by the user once this bit is set.
15
14
13
12
11
10
9876543210
OFFSET + 0
R
—
WI
L
TC
CM
———————
UN
CT
OFFSET + 2
DATA LENGTH
OFFSET + 4
TX DATA BUFFER POINTER
OFFSET + 6
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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