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When the transmit FIFO is loaded, synchronization and transmission begins depending on
the following:
¥ If a buffer is made ready before the SMC is enabled, the Þrst byte is placed in time
slot 1 if CLEN is 8 and to slot 2 if CLEN is greater than 8.
¥ If a buffer is made ready after its SMC is enabled, the Þrst byte can appear in any
time slot associated with this channel.
¥ If a buffer is closed with BD[L] set, then the next buffer can appear in any time slot
associated with this channel.
If the SMC runs out of transmit buffers and a new buffer is provided later, idles are sent in
the gap between buffers. Data transmission from the later buffer begins at the start of an
SMC time slot, but not necessarily the Þrst time slot after the frame sync. So, to maintain a
certain bit alignment beginning with the Þrst time slot, make sure that at least one TxBD is
always ready and that underruns do not occur. Otherwise, the SMC transmitter should be
disabled and reenabled. Section 30.2.4, ÒDisabling SMCs On-the-Fly,Ó describes how to
safely disable and reenable the SMC. Simply clearing and setting TEN may not be enough.
30.4.7 SMC Transparent Commands
Table 30-12 describes transmit commands issued to the CPCR.
Table 30-12. SMC Transparent Transmit Commands
Command
After hardware or software is reset and the channel is enabled in the SMCMR, the channel is in
STOP
transmit enable mode and polls the Þrst BD. This command disables transmission of frames on the
TRANSMIT
transmit channel. If the transparent controller receives this command while sending a frame, it stops
after the contents of the FIFO are sent (up to 2 characters). The TBPTR is not advanced to the next BD,
no new BD is accessed, and no new buffers are sent for this channel. The transmitter sends idles until
a
RESTART TRANSMIT
Starts or resumes transmission from the current TBPTR in the channel TxBD table. When the channel
RESTART
receives this command, it polls the R bit in this BD. The SMC expects this command after a
TRANSMIT
is issued. The channel is disabled in its mode register or after a transmitter error occurs. In
TRANSMIT
addition, the transmitter awaits resynchronization before transmission continues.
Initializes transmit parameters in this serial channel to reset state. Use only if the transmitter is
INIT TX
disabled. The
PARAMETERS
MOTOROLA
command is issued.
INIT TX AND RX PARAMETERS
Chapter 30. Serial Management Controllers
Part V. The Communications Processor Module
Description
command resets transmit and receive parameters.
STOP
30-25
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