XC886/888CLM
Serial Interfaces
User’s Manual
12-11
V1.3, 2010-02
Serial Interfaces, V 1.0
Baud rate in Mode 2
For UART module, the baud rate in mode 2 is dependent on the value of bit SMOD in
the PCON register. If SMOD = 0 (value after reset), the baud rate is 1/64 of the input
clock frequency
f
PCLK
. If SMOD = 1, the baud rate is 1/32 of
f
PCLK
.
(12.1)
For UART1 module, the baud rate in mode 2 does not depend on the bit SMOD and is
always 1/64 of the input clock frequency
f
PCLK
.
12.1.4.2
Dedicated Baud-rate Generator
Each of the UART modules has a dedicated baud-rate generator that is based on a
programmable 8-bit reload value, and includes divider stages (i.e., prescaler and
fractional divider) for generating a wide range of baud rates based on its input clock
f
PCLK
.
The baud rate timer is a count-down timer and is clocked by either the output of the
fractional divider (
f
MOD
) if the fractional divider is enabled (FDCON.FDEN = 1), or the
output of the prescaler (
f
DIV
) if the fractional divider is disabled (FDEN = 0). For baud rate
generation, the fractional divider must be configured to fractional divider mode
(FDCON.FDM = 0). This allows the baud rate control run bit BCON.R to be used to start
or stop the baud rate timer. At each timer underflow, the timer is reloaded with the 8-bit
reload value in register BG and one clock pulse is generated for the serial channel.
Enabling the fractional divider in normal divider mode (FDEN = 1 and FDM = 1) stops the
baud rate timer and nullifies the effect of bit BCON.R.
Register BG is a dual-function Baud-rate Generator/Reload register. Reading from BG
returns the timer’s contents, while writing to BG causes an auto-reload of its contents into
the baud rate timer if BCON.R = 1. If BCON.R = 0 at the time a write operation to BG
Field
Bits
Type Description
SMOD
7
rw
Double Baud Rate Enable
0
Do not double the baud rate of serial interface
in modes 1, 2 and 3.
1
Double the baud rate of serial interface in mode
2, and in modes 1 and 3 only if Timer 1 is used
as variable baud rate source.
0
1,[6:4] r
Reserved
Returns 0 if read; should be written with 0.
PCLK
f
64
SMOD
2
rate
baud
2
Mode
×
=
*
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