UART Modules
Freescale Semiconductor
26-17
MCF52235 ColdFire® Integrated Microcontroller Reference Manual, Rev. 6
26.4.1.1
Programmable Divider
n
transmitter and receiver can use the following clock sources:
•
An external clock signal on the DTIN
n
pin.
When not divided,
DTIN
n
provides a synchronous
clock; when divided by 16, it is asynchronous.
•
The internal bus clock supplies an asynchronous clock source divided by 32 and then divided by
the 16-bit value programmed in UBG1
n
and UBG2
n
. See
Section 26.3.11, “UART Baud Rate
Generator Registers (UBG1n/UBG2n)
The choice of DTIN or internal bus clock is programmed in the UCSR.
Figure 26-17. Clocking Source Diagram
NOTE
If DTIN
n
is a clocking source for the timer or UART, that timer module
cannot use DTIN
n
for timer input capture.
26.4.1.2
Calculating Baud Rates
The following sections describe how to calculate baud rates.
26.4.1.2.1
Internal Bus Clock Baud Rates
When the internal bus clock is the UART clocking source, it goes through a divide-by-32 prescaler and
then passes through the 16-bit divider of the concatenated UBG1
n
and UBG2
n
registers. The baud-rate
calculation is:
Eqn. 26-1
UART
On-Chip
TIN
÷
1
÷
16
16-bit
Divider
÷
32
TIN
Clocking sources programmed in UCSR
Timer Module
Internal
Tx
Rx
Rx Buffer
Tx Buffer
f
sys
Bus Clock
URXDn
UTXDn
DTINn
DTOUTn
Baudrate
f
sys
32 x Divider
[
]
------------------------------------
=
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
