UART Modules
Freescale Semiconductor
26-19
MCF52235 ColdFire® Integrated Microcontroller Reference Manual, Rev. 6
optional parity bit, and the programmed number of stop bits. The lsb is sent first. Data is shifted from the
transmitter output on the falling edge of the clock source.
After the stop bits are sent, if no new character is in the transmitter holding register, the UTXD
n
output
remains high (mark condition) and the transmitter empty bit (USR
n
[TXEMP]) is set. Transmission
resumes and TXEMP is cleared when the CPU loads a new character into the UART transmit buffer
(UTB
n
). If the transmitter receives a disable command, it continues until any character in the transmitter
shift register is completely sent.
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, UCTS
n
must be asserted for the character to be transmitted. If
UCTS
n
is negated in the middle of a transmission, the character in the shift register is sent and UTXD
n
remains in mark state until UCTS
n
is reasserted. If transmitter is forced to send a continuous low condition
by issuing a
SEND
BREAK
command, transmitter ignores the state of UCTS
n
.
If the transmitter is programmed to automatically negate URTS
n
when a message transmission completes,
URTS
n
must be asserted manually before a message is sent. In applications in which the transmitter is
disabled after transmission is complete and URTS
n
is appropriately programmed, URTS
n
is negated one
bit time after the character in the shift register is completely transmitted. The transmitter must be manually
reenabled by reasserting URTS
n
before the next message is sent.
shows the functional timing information for the transmitter.
Because
of
an
order
from
the
United
States
International
Trade
Commission,
BGA-packaged
product
lines
and
part
numbers
indicated
here
currently
are
not
available
from
Freescale
for
import
or
sale
in
the
United
States
prior
to
September
2010:MCF52234CVM60,
MCF52235CVM60
