Motorola MPC8260 - Manual (Page 721)

MOTOROLA Chapter 26. Serial Management Controllers (SMCs) 26-25
Part IV. Communications Processor Module
always ready and that underruns do not occur. Otherwise, the SMC transmitter should be
disabled and reenabled. Section 26.2.4, ÒDisabling SMCs On-the-Fly,Ó describes how to
safely disable and reenable the SMC. Simply clearing and setting TEN may not be enough.
26.4.6 SMC Transparent Commands
Table 26-10 describes transmit commands issued to the CPCR.
Table 26-11 describes receive commands issued to the CPCR.
26.4.7 Handling Errors in the SMC Transparent Controller
The SMC uses BDs and the SMCE to report message send and receive errors.
Table 26-10. SMC Transparent Transmit Commands
Command Description
STOP
TRANSMIT
After hardware or software is reset and the channel is enabled in the SMCM, the channel is in transmit
enable mode and polls the Þrst BD. This command disables transmission of frames on the 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 command is issued.
RESTART
TRANSMIT
Starts or resumes transmission from the current TBPTR in the channel TxBD table. When the channel
receives this command, it polls the R bit in this BD. The SMC expects this command after a
STOP
TRANSMIT is issued. The channel in its mode register is disabled or after a transmitter error occurs.
INIT TX
PARAMETERS
Initializes transmit parameters in this serial channel to reset state. Use only if the transmitter is
disabled. The
INIT TX AND RX PARAMETERS command resets transmit and receive parameters.
Table 26-11. SMC Transparent Receive Commands
Command Description
ENTER HUNT
MODE
Forces the SMC to close the current receive BD if it is in use and to use the next BD for subsequent
data. If the SMC is not receiving data, the buffer is not closed. Additionally, this command causes the
receiver to wait for a resynchronization before reception resumes.
CLOSE RXBD Forces the SMC to close the current receive BD if it in use and to use the next BD in the list for
subsequent received data. If the SMC is not in the process of receiving data, no action is taken.
i NIT RX
PARAMETERS
Initializes receive parameters in this serial channel to reset state. Use only if the receiver is disabled.
The
INIT TX AND RX PARAMETERS command resets receive and transmit parameters.
Table 26-12. SMC Transparent Error Conditions
Error Descriptions
Underrun The channel stops sending the buffer, closes it, sets UN in the BD, and generates a TXE interrupt if it is
enabled. The channel resumes sending after a RESTART TRANSMIT command. Underrun cannot occur
between frames.
Overrun The SMC maintains an internal FIFO for receiving data. If the buffer is in external memory, the CP begins
programming the SDMA channel when the Þrst character is received into the FIFO. If a FIFO overrun
occurs, the SMC writes the received data character over the previously received character. The previous
character and its status bits are lost. Then the channel closes the buffer, sets OV in the BD, and generates
the RXB interrupt if it is enabled. Reception continues as normal.