Serial Communication Controllers (SCCs)
MOTOROLA
MC68360 USER’S MANUAL
7-163
Rx Data Buffer Pointer
The receive buffer pointer, which always points to the first location of the associated data
buffer, may be even or odd. The buffer may reside in either internal or external memory.
7.10.16.17 UART 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 chan-
nel’s Tx BD table. The CP confirms transmission or indicates error conditions via the BDs to
inform the processor that the buffers have been serviced.
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.
W—Wrap (Final BD in Table)
0 = This is not the last BD in the Tx BD table.
1 = This is the last BD in the TxBD in the table. After this buffer has been used, the CP
will transmit data from the first BD in the table (the BD pointed to by TBASE). The
number of Tx BDs in this table is programmable, and is determined only by the W-
bit and the overall space constraints of the dual-port RAM.
I—Interrupt
0 = No interrupt is generated after this buffer has been serviced.
1 = The TX bit in the UART event register will be set when this buffer has been serviced
by the CP, which can cause an interrupt.
CR—Clear-to-Send Report
This bit allows a choice of either no delay between buffers transmitted in UART mode, or
a more accurate CTS lost error reporting and three bits of idle between buffers.
0 = The buffer following this buffer will be transmitted with no delay (assuming it is
ready), but the CT bit may not be set in the correct Tx BD or may not be set at all
in a CTS lost condition. Asynchronous flow control, however, continues to function
normally.
1 = Normal CTS lost (CT bit) error reporting, and three bits of idle occur between back-
to-back buffers.
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
OFFSET + 0
R
—
W
I
CR
A
CM
P
NS
—
—
—
—
—
—
CT
OFFSET + 2
DATA LENGTH
OFFSET + 4
TX DATA BUFFER POINTER
OFFSET + 6