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Communications Processor (CP)
Data Length
The data length is the number of octets that the V.110 controller has written to this BD
data buffer. It is written by the CP once as the BD is closed. The V.110 controller will write
nine bytes of data to the buffer. It will not write the all-zeros byte to the buffer.
The actual buffer size should be greater than or equal to 10
bytes.
Rx Buffer Pointer
This pointer contains the address of the associated data buffer. The buffer may reside in
either internal or external memory.
The Rx buffer pointer must be even, and the upper 8 bits of the
pointer must be zero for the function codes to operate correctly.
4.5.15.8 V.110 Transmit Buffer Descriptor (Tx BD)
Data is presented 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 M68000 core whether the buffers have been ser-
viced. The Tx BD is shown in Figure 4-41.
15
14
OFFSET + 0
E
X
OFFSET + 2
OFFSET + 4
OFFSET +6
The first word contains status and control bits. Bits 15–10 are prepared by the user before
transmission. Bit 1 is set by the V.110 controller after the buffer has been transmitted. Bit 15
is set by the user and cleared by the V.110 controller.
R—Ready
0 = This buffer is not currently ready for transmission. The user is free to manipulate
this BD and its associated buffer. The V.110 controller clears this bit after the buffer
has been fully transmitted (or after an error condition is encountered).
1 = The data buffer has been prepared for transmission by the user (but not yet trans-
mitted). No fields of this BD may be written by the user once this bit is set.
X—External Buffer
0 = The buffer associated with this BD is in internal dual-port RAM.
1 = The buffer associated with this BD is in external memory.
4-120
13
12
11
10
W
I
L
0
TX BUFFER POINTER (24-bits used, upper 8 bits must be 0)
Figure 4-41. V.110 Transmit Buffer Descriptor
MC68302 USER'S MANUAL
NOTE
NOTE
9
8
7
6
—
—
—
—
DATA LENGTH
5
4
3
2
—
—
—
—
MOTOROLA
1
0
UN
—
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