Motorola PowerQUICC II MPC8280 Series Reference Manual page 927

• If a buffer is made ready when the SMC2 is enabled, the first byte is placed in time
slot 1 if CLSN is 8 and to slot 2 if CLSN is 16.
• If a buffer has its SMC enabled, then the first byte in the next buffer can appear in
any time slot associated with this channel.
• If a buffer is ended with the L bit 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 first time slot after the frame sync. So, to maintain a
certain bit alignment beginning with the first 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 28.2.4, "Disabling SMCs On-the-Fly," describes how to
safely disable and reenable the SMC. Simply clearing and setting TEN may not be enough.
28.4.6 SMC Transparent Commands
Table 28-10 describes transmit commands issued to the CPCR.
Table 28-10. SMC Transparent Transmit Commands
Command
After hardware or software is reset and the channel is enabled in the SMCM, the channel is in transmit
STOP
enable mode and polls the first 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
command is issued.
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 in its mode register is disabled or after a transmitter error occurs.
TRANSMIT
Initializes transmit parameters in this serial channel to reset state. Use only if the transmitter is disabled.
INIT TX
The
PARAMETERS INIT TX AND RX PARAMETERS
Table 28-11 describes receive commands issued to the CPCR.
Table 28-11. SMC Transparent Receive Commands
Command
Forces the SMC to close the current receive BD if it is in use and to use the next BD for subsequent data.
ENTER HUNT
If the SMC is not receiving data, the buffer is not closed. Additionally, this command causes the receiver
MODE
to wait for a resynchronization before reception resumes.
Forces the SMC to close the current receive BD if it in use and to use the next BD in the list for
CLOSE RXBD
subsequent received data. If the SMC is not in the process of receiving data, no action is taken.
i Initializes receive parameters in this serial channel to reset state. Use only if the receiver is disabled.
NIT RX
The
PARAMETERS INIT TX AND RX PARAMETERS
MOTOROLA
Freescale Semiconductor, Inc.
command resets transmit and receive parameters.
command resets receive and transmit parameters.
Chapter 28. Serial Management Controllers (SMCs)
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SMC in Transparent Mode
Description
Description
RESTART
STOP
28-27