Uart Command Set - Motorola MC68302 User Manual

than being interrupted after the reception of each character, a terminal driver
may want to wait until an end-of-line character has been typed by a user
before handling the input data.
As another example, when transmitting ASCII files, the data may be trans-
ferred as messages ending on the end-of-line character. Each message could
be both transmitted and received as a linked list of buffers without any
intervention from the M68000 core. This technique achieves both ease in
programming and significant savings in processor overhead.
On the receive side, the user may define up to eight control characters. Each
control character may be configured to designate the end of a message (such
as end of line) or to generate a maskable interrupt without being stored in
the data buffer. This latter option is useful when flow-control characters such
as XON or XOFF need to alert the M68000 core, yet do not belong to the
message being received.
In the message-oriented environment, the data stream is divided into buffers.
However, the physical format of each character (stop bits, parity, etc.) is not
altered.
4.5.11.5 UART COMMAND SET.
These commands are issued to the command
register described in 4.3 COMMAND SET.
STOP TRANSMIT Command
After a hardware or software reset and the enabling of the channel by
writing the
sec
mode register, the channel is in the transmit enable mode
and starts polling the first BD in the table.
The channel STOP TRANSMIT command disables the transmission of char-
acters on the transmit channel. If this command is received by the UART
controller during message transmission, transmission of that message is
aborted. No new BD is accessed, and no new characters are transmitted
for this channel.
The UART transmitter will transmit a programmable number of break se-
quences and then start to transmit idles. The number of break sequences
(which may be zero) should be written to the break count register (BRKCR)
before this command is given to the UART controller.
The STOP TRANSMIT command must be issued before the SCC mode
register is used to disable the transmitter if the transmitter will be re-
enabled at a later time.
MOTOROLA MC68302 USER'S MANUAL 4-37