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UART Modules
MCF5272 ColdFire
®
Integrated Microprocessor User’s Manual, Rev. 3
Freescale Semiconductor
16-23
If the transmitter is reset through a software command, operation stops immediately (see
“UART Command Registers (UCRn)
”). The transmitter is reenabled through the UCR
n
to resume
operation after a disable or software reset.
If the clear-to-send operation is enabled, CTS must be asserted for the character to be transmitted. If CTS
is negated in the middle of a transmission, the character in the shift register is sent and TxD remains in
mark state until CTS is reasserted. If the transmitter is forced to send a continuous low condition by issuing
a
START
BREAK
command, the transmitter ignores the state of CTS.
If the transmitter is programmed to automatically negate RTS when a message transmission completes,
RTS must be asserted manually before a message is sent. In applications in which the transmitter is
disabled after transmission is complete and RTS is appropriately programmed, RTS is negated one bit time
after the character in the shift register is completely transmitted. The transmitter must be manually
reenabled by reasserting RTS before the next message is to be sent.
The transmitter must be enabled prior to accepting a
START
BREAK
command. If the transmitter is disabled
while the BREAK is active, the BREAK is not terminated. The BREAK can only be terminated by using
the
STOP
BREAK
command.
shows the functional timing information for the transmitter.
Figure 16-25. Transmitter Timing
C1
1
C2
C3
Break
C4
C6
TxD
Transmitter
Enabled
USR
n
[TxRDY]
W
2
W
W
W
W
W
W
W
CTS
3
RTS
4
Manually asserted
by
BIT
-
SET
command
Manually
asserted
Start
break
C5
not
transmitted
C6
C4
Stop
break
C3
C2
C1
1
C1 in transmission
3
UMR2
n
[TxCTS] = 1
1
C
n
= transmit characters
2
W = write
4
UMR2
n
[TxRTS] = 1
internal
module
select