Serial Communication Controllers (SCCs)
MOTOROLA
MC68360 USER’S MANUAL
7-205
sequence. The EOT sequence should be the first buffer presented to the BISYNC controller
for transmission after re-enabling transmission.
NOTE
The BISYNC controller will remain in the transparent or normal
mode after receiving the STOP TRANSMIT or RESTART
TRANSMIT commands.
GRACEFUL STOP TRANSMIT Command
.
The channel GRACEFUL STOP TRANSMIT
command is used to stop transmission in an orderly way rather than abruptly, as performed
by the regular STOP TRANSMIT command. It stops transmission after the current frame has
completed transmission, or immediately if there is no frame being transmitted. The GRA bit
in the SCCE will be set once transmission has stopped. After transmission ceases, the
BISYNC 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 BISYNC
controller after a STOP TRANSMIT command, after a STOP TRANSMIT command and dis-
abling the channel in its SCC mode register, after a GRACEFUL STOP TRANSMIT com-
mand, or after a transmitter error (underrun or CTS lost). The BISYNC controller will resume
transmission from the current TBPTR in the channel’s Tx BD table.
INIT TX PARAMETERS Command
.
Initializes all the transmit parameters in this serial chan-
nel’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.
7.10.20.5.2 Receive Commands.
The following paragraphs describe the BISYNC receive
commands.
RESET BCS CALCULATION Command
.
The RESET BCS CALCULATION command
resets the receive BCS accumulator immediately. For example, it may be used to reset the
BCS after recognizing a control character (such as SOH), signifying that a new block is com-
mencing.
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 the receive enable mode and will use
the first BD in the table.
The ENTER HUNT MODE command is used to force the BISYNC controller to abort recep-
tion of the current block and enter the hunt mode. In the hunt mode, the BISYNC controller
continually scans the input data stream for the SYN1–SYN2 sequence as programmed in
the data synchronization register. After receiving the command, the current receive buffer is
closed, and the BCS is reset. Message reception continues using the next BD.