Freescale Semiconductor, Inc.
Start Break—The start break command forces the channel's TxDx low. If the transmitter
is empty, the start of the break conditions can be delayed up to one bit time. If the
transmitter is active, the break begins when transmission of the character is complete. If
a character is in the transmitter shift register, the start of the break is delayed until the
character is transmitted. If the transmitter holding register has a character, that
character is transmitted after the break. The transmitter must be enabled for this
command to be accepted. The state of the CTS≈ input is ignored for this command.
Stop Break—The stop break command causes the channel's TxDx to go high (mark)
within two bit times. Characters stored in the transmitter buffer, if any, are transmitted.
Assert RTS—The assert RTS command forces the channel's RTS≈ output low.
Negate RTS—The negate RTS command forces the channel's RTS≈ output high.
TC1–TC0—Transmitter Commands
These bits select a single command as listed in Table 7-7.
Table 7-7. TCx Control Bits
TC1
0
TC0
0
Command
No Action Taken
Enable Transmitter
Disable Transmitter
Do Not Use
0
1
1
0
1
1
No Action Taken—The no action taken command causes the transmitter to stay in its
current mode. If the transmitter is enabled, it remains enabled; if disabled, it remains
disabled.
Transmitter Enable—The transmitter enable command enables operation of the
channel's transmitter. The TxEMP and TxRDY bits in the SR are also set. If the
transmitter is already enabled, this command has no effect.
Transmitter Disable—The transmitter disable command terminates transmitter operation
and clears the TxEMP and TxRDY bits in the SR. However, if a character is being
transmitted when the transmitter is disabled, the transmission of the character is
completed before the transmitter becomes inactive. If the transmitter is already
disabled, this command has no effect.
Do Not Use—Do not use this bit combination because the result is indeterminate.
MOTOROLA
MC68340 USER’S MANUAL
7- 29
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