Freescale Semiconductor MPC8260 - Manual (Page 710)

SCC UART Mode
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
21-6 Freescale Semiconductor
21.7 SCC UART Commands
The transmit commands in Table 21-2 are issued to the CP command register (CPCR).
Receive commands are described in Table 21-3 .
21.8 Multidrop Systems and Address Recognition
In multidrop systems, more than two stations can be on a network, each with a specific address.
Figure 21-2 shows two examples of this configuration. Frames made up of many characters can be
broadcast as long as the first character is the destination address. The UART frame is extended by one bit
to distinguish an address character from standard data characters. Programmed in PSMR[UM], the
controller supports the following two multidrop modes:
Table 21-2. 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 21-3. 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.