Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 822

Serial Management Controllers (SMCs)
Table 29-15 describes SMC transparent TxBD fields.
Bits Name
0 R Ready.
0 The buffer is not ready for transmission. The BD and buffer can be updated. The CP clears R after
the buffer is sent or after an error occurs.
1 The user-prepared buffer is not sent or is being sent. BD fields must not be updated if R is set.
1 — Reserved, should be cleared.
2 W Wrap (final BD in table).
0 Not the last BD in the table.
1 Last BD in the table. After this buffer is used, the CP transmits outgoing data from the first BD that
TBASE points to. The number of TxBDs in this table is programmable and determined by the W
bit.
3 I Interrupt.
0 No interrupt is generated after this buffer is serviced unless an error occurs.
1 SMCE[TX] or SMCE[TXE] are set when the buffer is serviced. They can cause interrupts if they
are enabled.
Note that this bit does not mask SMCE[TXE].
4 L Last in message.
0 The last byte in the buffer is not the last byte in the transmitted transparent frame. Data from the
next transmit buffer (if ready) is sent immediately after the last byte of this buffer.
1 The last byte in this buffer is the last byte in the transmitted transparent frame. After this buffer is
sent, the transmitter requires synchronization before the next buffer is sent.
5 — Reserved, should be cleared.
6 CM Continuous mode.
0 Normal operation.
1 The CP does not clear R after this BD is closed, allowing the buffer to be automatically resent
when the CP accesses this BD again. However, the R bit is cleared if an error occurs during
transmission, regardless of how CM is set.
7–13 — Reserved, should be cleared.
14 UM Underrun. Set when the SMC encounters a transmitter underrun condition while sending the buffer.
15 — Reserved, should be cleared.
Data length represents the number of octets the CP should transmit from this buffer. It is never modified
by the CP. The data length can be even or odd, but if the number of bits in the transparent character is
greater than 8, the data length should be even. For example, to transmit three transparent 8-bit characters,
the data length field should be initialized to 3. However, to transmit three transparent 9-bit characters, the
data length field should be initialized to 6 because the three 9-bit characters occupy three half words in
memory.
The buffer pointer points to the first byte of the buffer. They can be even or odd, unless character length is
greater than 8 bits, in which case the transmit buffer pointer must be even. For instance, the pointer to 8-bit
transparent characters can be even or odd, but the pointer to 9-bit transparent characters must be even. The
buffer can reside in internal or external memory.
29-28
Table 29-15. SMC Transparent TxBD Field Descriptions
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Description
Freescale Semiconductor