Motorola MC68302 User Manual page 174

sequence. The EOT sequence should be the first buffer presented to the
BISYNC controller for transmission after re-enabling transmission.
The STOP TRANSMIT command must be issued before the SCC mode
register is used to disable the transmitter if the transmitter is to be re-
enabled at a later time.
NOTE
The BISYNC controller will remain in the transparent or normal mode
after receiving the STOP TRANSMIT or RESTART TRANSMIT com-
mands.
RESTART TRANSMIT Comand
The RESTART TRANSMIT command is used to begin or resume transmis-
sion from the current Tx BD number (TBD#) in the channel's Tx BD table.
When this command is received by the channel, it will start polling the
ready bit in this BD. This command is expected by the BISYNC controller
after a STOP TRANSMIT command, after the STOP TRANSMIT command
and the disabling of the channel in its mode register, or after a transmitter
error (underrun or CTS lost) occurs.
If the transmitter is being re-enabled, the RESTART TRANSMIT command
must be used and should be followed by the enabling of the transmitter
in the
sec
mode register.
RESET BCS CALCULATION Command
The RESET BCS CALCULATION command resets the receive BCS accu-
mulator immediately. For example, it may be used to reset the BCS after
recognizing a control character, signifying that a new block is commencing
(such as SOH).
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 BO in the table.
The ENTER HUNT MODE command is used to force the BISYNC controller
to abort reception of the current block and enter the hunt mode. In the
hunt mode, the BISYNC controller continually scans the input data stream
for the SYN 1-SYN2 sequence as programed 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 BO.
MOTOROLA MC68302 USER'S MANUAL 4-71