SCC UART Mode
MPC885 PowerQUICC Family Reference Manual, Rev. 2
22-6
Freescale Semiconductor
characters such as XON or XOFF are needed but are not part of the received message. See
Section 22.9,
“Receiving Control Characters.”
22.6
Error and Status Reporting
Overrun, parity, noise, and framing errors are reported via the BDs and/or error counters in the UART
parameter RAM. Signal status is indicated in the status register; a maskable interrupt is generated when
status changes.
22.7
SCC UART Commands
The transmit commands in
Table 22-2
are issued to the CP command register (CPCR).
Receive commands are described in
Table 22-3
.
Table 22-2. Transmit Commands
Command
Description
STOP
TRANSMIT
After a hardware or software reset and a channel is enabled in the GSMR, the transmitter starts polling
the first BD in the TxBD table every 8 Tx clocks.
STOP
TRANSMIT
disables character transmission. If the
SCC receives
STOP
TRANSMIT
as a message is being sent, the message is aborted. The transmitter
finishes sending data transferred to its FIFO and stops. The TBPTR is not advanced. The UART
transmitter sends a programmable break sequence and starts sending idles. The number of break
characters in the sequence (which can be zero) should be written to BRKCR in the parameter RAM
before issuing this command.
GRACEFUL
STOP
TRANSMIT
Used to stop transmitting smoothly. The transmitter stops after the current buffer has been completely
sent or immediately if no buffer is being sent. SCCE[GRA] is set once transmission stops, then the
UART Tx parameters, including the TxBD, can be modified. TBPTR points to the next TxBD in the table.
Transmission begins once the R bit of the next BD is set and a
RESTART
TRANSMIT
command is issued.
RESTART
TRANSMIT
Enables transmission. The controller expects this command after it disables the channel in its PSMR,
after a
STOP
TRANSMIT
command, after a
GRACEFUL
STOP
TRANSMIT
command, or after a transmitter
error. Transmission resumes from the current BD.
INIT
TX
PARAMETERS
Resets the transmit parameters in the parameter RAM. Issue only when the transmitter is disabled.
Note that
INIT
TX
AND
RX
PARAMETERS
resets both Tx and Rx parameters.
Table 22-3. Receive Commands
Command
Description
ENTER
HUNT
MODE
Forces the receiver to close the RxBD in use and enter hunt mode. After a hardware or software reset,
once an SCC is enabled in the GSMR, the receiver is automatically enabled and uses the first BD in
the RxBD table. If a message is in progress, the receiver continues receiving in the next BD. In
multidrop hunt mode, the receiver continually scans the input data stream for the address character.
When it is not in multidrop mode, it waits for the idle sequence (one character of idle). Data present in
the Rx FIFO is not lost when this command is executed.
CLOSE
RXBD
Forces the SCC to close the RxBD in use and use the next BD for subsequent received data. If the
SCC is not in the process of receiving data, no action is taken.
Note that in an SCC UART controller,
CLOSE
RXBD
functions like
ENTER
HUNT
MODE
but does not need
to receive an idle character to continue receiving.
INIT
RX
PARAMETERS
Resets the receive parameters in the parameter RAM. Should be issued when the receiver is disabled.
Note that
INIT
TX
AND
RX
PARAMETERS
resets both Tx and Rx parameters.
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