
MOTOROLA
Chapter 26. SCC BISYNC Mode
26-5
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
SCC BISYNC Commands
The controller can be programmed so software handles the rst two or three bytes.
The controller directly handles subsequent data without interrupting the core.
26.5 SCC BISYNC Commands
Transmit and receive commands are issued to the CP command register (CPCR). Transmit
Table 26-2. 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 rst 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 ushed. 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 rst 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 nishes 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 modied. 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 26-3. 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 rst 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.