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Communications Processor (CP)
4-96
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= Either TX or TXE in the BISYNC event register will be set when this buffer has been
serviced by the CP, which can cause an interrupt.
L—Last in Message
0 = The last character in the buffer is not the last character in the current block.
1 = The last character in the buffer is the last character in the current block. The trans-
mitter will enter (remain in) normal mode after sending the last character in the buff-
er and the BCS (if enabled).
TB—Transmit BCS
This bit is valid only when the L bit is set.
0 = Transmit the SYN1–SYN2 sequence or IDLE (according to the SYNF bit in the BI-
SYNC mode register) after the last character in the buffer.
1 = Transmit the BCS sequence after the last character. The BISYNC controller will
also reset the BCS generator after transmitting the BCS sequence.
B—BCS Enable
0 = Buffer consists of characters to be excluded from the BCS accumulation.
1 = Buffer consists of characters to be included in the BCS accumulation.
BR—BCS Reset
0 = The BCS accumulation is not reset.
1 = The transmitter BCS accumulation is reset (used for STX or SOH) before sending
the data buffer.