
Communications Processor (CP)
4-132
MC68302 USER’S MANUAL
MOTOROLA
R—Ready
0 = This buffer is not currently ready for transmission. The user is free to manipulate
this BD (or its associated buffer). The CP clears this bit after the buffer has been
fully transmitted or after an error condition has been 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.
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 Tx BD table. After this buffer has been used, the CP will
transmit data from the first BD in the table.
NOTE
The user is required to set the wrap bit in one of the first eight
BDs; otherwise, errant behavior may occur.
I—Interrupt
0 = No interrupt is generated after this buffer has been serviced.
1 = When this buffer is serviced by the CP, the TX or TXE bit in the transparent event
register will be set, which can cause an interrupt.
L—Last in Message
0 = The last byte in the buffer is not the last byte in the transmitted block. Data from the
next transmit buffer (if ready) will be transmitted immediately following the last byte
of this buffer.
1 = The last byte in the buffer is the last byte in the transmitted block. After this buffer
is transmitted, the transmitter will require synchronization before the next buffer
can be transmitted.
Bits 10—2 are reserved for future use; they should be written with zero.
The following status bits are written by the CP after it has finished transmitting the associat-
ed data buffer.
UN—Underrun
The transparent controller encountered a transmitter underrun condition while transmit-
ting the associated data buffer.
CT—CTS Lost
CTS in NMSI mode or L1GR in IDL/GCI mode was lost during frame transmission.