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Part IV. Communications Processor Module
26.3.3 SMC UART Channel Reception Process
When the core enables the SMC receiver, it enters hunt mode and waits for the Þrst
character. The CP then checks the Þrst RxBD to see if it is empty and starts storing
characters in the buffer. When the buffer is full or the MAX_IDL timer expires (if enabled),
the SMC clears the E bit in the BD and generates an interrupt if the I bit in the BD is set. If
incoming data exceeds the bufferÕs length, the SMC fetches the next BD, and, if it is empty,
continues transferring data to this BDÕs buffer. If CM is set in the RxBD, the E bit is not
cleared, so the CP can overwrite this buffer on its next access.
26.3.4 Programming the SMC UART Controller
UART mode is selected by setting SMCMR[SM] to 0b10. See Section 26.2.1, ÒSMC Mode
Registers (SMCMR1/SMCMR2).Ó UART mode uses the same data structure as other
modes. This structure supports multibuffer operation and allows break and preamble
sequences to be sent. Overrun, parity, and framing errors are reported via the BDs. At its
simplest, the SMC UART controller functions in a character-oriented environment,
whereas each character is sent with the selected stop bits and parity. They are received into
separate 1-byte buffers. A maskable interrupt can be generated when each buffer is
received.
Many applications can take advantage of the message-oriented capabilities that the SMC
UART supports through linked buffers for sending or receiving. Data is handled in a
message-oriented environment, so entire messages can be handled instead of individual
characters. A message can span several linked buffers; each one can be sent and received as
a linked list of buffers without core intervention, which simpliÞes programming and saves
processor overhead. In a message-oriented environment, an idle sequence is used as the
message delimiter. The transmitter can generate an idle sequence before starting a new
message and the receiver can close a buffer when an idle sequence is found.
26.3.5 SMC UART Transmit and Receive Commands
Table 26-4 describes transmit commands issued to the CPCR.
Command
Disables transmission of characters on the transmit channel. If the SMC UART controller receives this
STOP
command while sending a message, it stops sending. The SMC UART controller Þnishes sending any
TRANSMIT
data that has already been sent to its FIFO and shift register and then stops sending data. The TBPTR
is not advanced when this command is issued. The SMC UART controller sends a programmable
number of break sequences and then sends idles. The number of break sequences, which can be
zero, should be written to the BRKCR before this command is issued to the SMC UART controller.
Enables characters to be sent on the transmit channel. The SMC UART controller expects it after
RESTART
disabling the channel in its SMCMR and after issuing the
TRANSMIT
controller resumes transmission from the current TBPTR in the channelÕs TxBD table.
Initializes transmit parameters in this serial channelÕs parameter RAM to their reset state and should
INIT TX
only be issued when the transmitter is disabled. The
PARAMETERS
used to reset the transmit and receive parameters.
26-12
Table 26-4. Transmit Commands
Description
MPC8260 PowerQUICC II UserÕs Manual
command. The SMC UART
STOP TRANSMIT
and
INIT TX
RX PARAMETERS
command can also be
MOTOROLA
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