Freescale Semiconductor MPC8260 - Manual (Page 894)

Multi-Channel Controllers (MCCs)
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
28-46 Freescale Semiconductor
Table 28-23 describes TxBD fields.
0 1 2 3 4 5 6 7 8 9 10 11 12 15
Offset + 0 R RT
1
W I L TC CM — UB — SUD
1
PAD
Offset + 2 Data Length
Offset + 4 Tx Data Buffer Pointer
Offset + 6
1
SS7 mode only. Otherwise, reserved.
Figure 28-22. MCC Transmit Buffer Descriptor (TxBD)
Table 28-23. TxBD Field Descriptions
Bits Name Description
0 R Ready
0 The 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 is ready to be transmitted. The transmission may have begun, but it has not
completed. The user cannot modify this BD once this bit is set.
1 RT SS7 mode only: Retransmit.
0 Normal operation
1 The CP repeats transmission of this BD until the RT bit is cleared. After the RT bit is cleared the
CP advances to the next BD in the table. This feature is useful for automatic LSSU
retransmission.
Note: This bit is reserved in all other modes of operation.
2 W Wrap (final BD in table)
0 This is not the last BD in the TxBD table.
1 This is the last BD in the TxBD table. After this buffer is used, the CP receives incoming data into
the first BD in the table (the BD pointed to by TBASE). The number of TxBDs in this table is
programmable and is determined the wrap bit.
3 I Interrupt
0 No interrupt is generated after this buffer has been serviced.
1 The TXB bit in the event register is set when this buffer is serviced. TXB can cause an interrupt
if enabled.
4 L Last
0 This is not the last buffer in the frame.
1 This is the last buffer in the current frame.
5 TC Tx CRC. Valid only when L = 1. Otherwise it is ignored.
0 Transmit the closing flag after the last data byte. This setting can be used for testing purposes to
send an erroneous CRC after the data.
1 Transmit the CRC sequence after the last data byte.
6 CM Continuous mode
0 Normal operation.
1 The CP does not clear the ready bit after this BD is closed, allowing the associated data buffer to
be retransmitted automatically when the CP next accesses this BD. However, the R bit is cleared
if an error occurs during transmission, regardless of the CM bit setting.
7 — Reserved, should be cleared.