Serial Communication Controllers (SCCs)
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MC68360 USER’S MANUAL
MOTOROLA
already transferred to its FIFO and then stops transmitting data. The TBPTR is not
advanced.
The UART transmitter will transmit a programmable number of break sequences and then
start to transmit idles. The number of break sequences (which may be zero) should be writ-
ten to the break count register before this command is given to the UART controller.
GRACEFUL STOP TRANSMIT Command
.
The GRACEFUL STOP TRANSMIT command
is used to stop transmission in an orderly way rather than abruptly, as performed by the reg-
ular STOP TRANSMIT command. It stops transmission after the current buffer has com-
pleted transmission, or immediately if there is no buffer being transmitted. The GRA bit in
the SCCE will be set once transmission has stopped. After transmission ceases, the UART
transmit parameters, including BDs, may be modified. The TBPTR will point to the next Tx
BD in the table. Transmission will begin once the R-bit of the next BD is set and the
RESTART TRANSMIT command is issued.
RESTART TRANSMIT Command
.
The RESTART TRANSMIT command enables the trans-
mission of characters on the transmit channel. This command is expected by the UART con-
troller after disabling the channel in its SCC mode register, after a STOP TRANSMIT
command, after a GRACEFUL STOP TRANSMIT command, or after a transmitter error
(underrun or CTS lost). The UART controller will resume transmission from the current
TBPTR in the channel’s Tx BD table.
INIT TX PARAMETERS Command. This command initializes all transmit parameters in this
serial channel’s parameter RAM to their reset state. This command should only be issued
when the transmitter is disabled. Note that the INIT TX; AND RX PARAMETERS command
may also be used to reset both transmit and receive parameters.
7.10.16.6.2 Receive Commands.
The following paragraphs describe the UART receive
commands.
ENTER HUNT MODE ENTER HUNT MODE;Command
.
After a hardware or software reset
and the enabling of the channel in the SCC mode register, the channel is in receive enable
mode and will use the first BD in the table.
The ENTER HUNT MODE command is used to force the UART controller to close the cur-
rent Rx BD if it is being used and enter the hunt mode. The UART controller will resume
reception to the next BD if a message was in progress.
In the multidrop hunt mode, the UART controller continually scans the input data stream for
the address character. When not in multidrop mode, the UART controller will wait for the idle
sequence (one character of idle) without losing any data that was in the receive FIFO when
this command was executed.
CLOSE Rx BD Command
.
The CLOSE Rx BD command is used to force the SCC to close
the Rx BD, if it is currently being used, and to use the next BD for any subsequent data that
is received. If the SCC is not in the process of receiving data, no action is taken by this com-
mand.