Motorola MPC8260 - Manual (Page 915)

MOTOROLA Chapter 31. FCC HDLC Controller 31-13
Part IV. Communications Processor Module
Table 31-8 describes HDLC TxBD Þelds.
The TxBD status bits are written by the HDLC controller after sending the associated data
buffer.
Table 31-8. HDLC TxBD Field Descriptions
Bits Name Description
0 R Ready
0 The buffer associated with this BD is not ready for transmission. The user can manipulate this
BD or its associated buffer. The CP clears R after the buffer has been sent or an error occurs.
1 The buffer is ready to be sent. The transmission may have begun, but it has not completed. The
user cannot set Þelds in this BD once R is set.
1 Ñ Reserved, should be cleared.
2 W Wrap (Þnal BD in table)
0 Not the last BD in the TxBD table.
1 Last BD in the TxBD table. After this buffer has been used, the CP sends data from the Þrst BD
that TBASE points to in the table. The number of TxBDs in this table is determined only by the
W bit and the overall space constraints of the dual-port RAM.
3 I Interrupt
0 No interrupt is generated after this buffer is serviced.
1 Either FCCE[TXB] or FCCE[TXE] is set when this buffer is serviced by the HDLC controller.
These bits can cause interrupts if they are enabled.
4 L Last
0 Not the last buffer in the frame.
1 Last buffer in the current frame.
5 TC Tx CRC.Valid only when the L bit is set. Otherwise, it is ignored.
0 Transmit the closing ßag after the last data byte. This setting can be used to send a bad CRC
after the data for testing purposes.
1 Transmit the CRC sequence after the last data byte.
6 CM Continuous mode
0 Normal operation.
1 The R bit is not cleared by the CP after this BD is closed, allowing the buffer to be retransmitted
automatically the next time the CP accesses this BD. However, the R bit is cleared if an error
occurs during transmission, regardless of the CM bit.
7Р13 С Reserved, should be cleared.
14 UN Underrun. The HDLC controller encounters a transmitter underrun condition while sending the
buffer. The HDLC controller writes UN after sending the buffer.
15 CT CTS lost. Set when CTS is lost during frame transmission in NMSI mode. If data from more than
one buffer is in the FIFO buffer when this error occurs, CT is set in the currently open TxBD. The
HDLC controller writes CT after sending the buffer.