Freescale Semiconductor MPC8260 - Manual (Page 755)

SCC BISYNC Mode
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
Freescale Semiconductor 23-5
Receive commands are described in Table 23-3 .
23.6 SCC BISYNC Control Character Recognition
The BISYNC controller recognizes special control characters that customize the protocol implemented by
the BISYNC controller and aid its operation in a DMA-oriented environment. They are used for receive
buffers longer than one byte. In single-byte buffers, each byte can be easily inspected so control character
recognition should be disabled.
Table 23-2. Transmit Commands
Command Description
STOP TRANSMIT After hardware or software is reset and the channel is enabled in the GSMR, the channel is in
transmit enable mode and starts polling the first BD every 64 transmit clocks. This command stops
transmission after a maximum of 64 additional bits without waiting for the end of the buffer and the
transmit FIFO to be flushed. TBPTR is not advanced, no new BD is accessed, and no new buffers
are sent for this channel. SYNC–SYNC or DLE–SYNC pairs are sent continually until a
RESTART
TRANSMIT is issued. A STOP TRANSMIT can be used when an EOT sequence should be sent and
transmission should stop. After transmission resumes, the EOT sequence should be the first buffer
sent to the controller.
Note that the controller remains in transparent or normal mode after it receives a
STOP TRANSMIT or
RESTART TRANSMIT command.
GRACEFUL STOP
TRANSMIT
Stops transmission after the current frame finishes sending or immediately if there is no frame being
sent. SCCE[GRA] is set once transmission stops. Then BISYNC transmit parameters and TxBDs
can be modified. The TBPTR points to the next TxBD. Transmission resumes when the R bit of the
next BD is set and a
RESTART TRANSMIT is issued.
RESTART
TRANSMIT
Lets characters be sent on the transmit channel. The BISYNC controller expects it after a STOP
TRANSMIT or a GRACEFUL STOP TRANSMIT command is issued, after a transmitter error occurs, or after
a STOP TRANSMIT is issued and the channel is disabled in its SCCM. The controller resumes
transmission from the current TBPTR in the channel’s TxBD table.
INIT TX
PARAMETERS
Initializes all transmit parameters in the serial channel’s parameter RAM to their reset state. Issue
only when the transmitter is disabled.
INIT TX AND RX PARAMETERS resets transmit and receive
parameters.
Table 23-3. Receive Commands
Command Description
RESET BCS
CALCULATION
Immediately resets the receive BCS accumulator. It can be used to reset the BCS after recognizing
a control character, thus signifying that a new block is beginning.
ENTER HUNT
MODE
After hardware or software is reset and the channel is enabled in SCCM, the channel is in receive
enable mode and uses the first BD. This command forces the controller to stop receiving and enter
hunt mode, during which the controller continually scans the data stream for an SYN1–SYN2
sequence as programmed in the DSR. After receiving the command, the current receive buffer is
closed and the BCS is reset. Message reception continues using the next BD.
CLOSE RXBD Used to force the SCC to close the current RxBD if it is in use and to use the next BD for subsequent
data. If data is not being received, no action is taken.
INIT RX
PARAMETERS
Initializes receive parameters in this serial channel’s parameter RAM to reset state. Issue only when
the receiver is disabled. An
INIT TX AND RX PARAMETERS resets transmit and receive parameters.