MMUART Peripherals
UG0331 User Guide Revision 15.0
492
13.4.4
Baud Rate Divisor Registers
Baud rate clock can be generated in three modes: Asynchronous mode, Synchronous Master mode, and
Synchronous Slave mode. Apart from this, MMUART has an option of generating a fractional baud rate
that provides more precision. For more details refer to the
13.4.4.1 Asynchronous/Synchronous Mode Context
In Asynchronous mode, the baud rate (BR) clock is generated by dividing the input reference clock's
frequency (APB_0_CLK for MMUART_0 and APB_1_CLK for MMUART_1) by 16 and the integer plus
fractional divisor value, as shown below.
Divisor Value = Integer Value (DMR + DLR registers) plus Fractional Value (DFR/64).
In the Synchronous-Master mode, the baud rate clock is generated by dividing the input reference clock's
frequency (APB_0_CLK for MMUART_0 and APB_1_CLK for MMUART_1) by 2 and the integer divisor
value, as shown below.
DivisorValue = Integer Value (DMR + DLR registers).
In the Synchronous Slave mode, the baud rate clock is generated directly from the input clock, and as
such the divisor registers are not used.
Note:
The maximum input clock frequency is 1/2 APB_X_CLK (master clock) frequency, if input filtering is not
used. If input filtering is used, then the maximum input clock frequency is determined by the following
equation:
The glitch filter length (GLR) can be configured by setting the bits in glitch filter register (
13.4.4.2 Fractional Baud Rate Register
The baud rate divisor value is a 22-bit number consisting of a 16-bit integer and a 6-bit fractional part.
This is used by the baud rate generator to determine the bit period. The fractional baud rate divider
enables the use of any clock with a frequency >3.6864MHz to act as input clock, while it is still possible to
generate all the standard baud rates. The 16-bit integer is written to the integer baud rate register (
).
The 6-bit fractional part is written to the fractional baud rate register (
s are accomplished for
divisor values greater than one using time averaging of the two nearest integer value baud rates based
on the fractional value in the
:
EQ 1
1
CLEAR_RX_FIFO
W
0
Clears all bytes in Rx FIFO and resets counter logic. This
shift register is not cleared.
0: Disabled (default)
1: Enabled
0
ENABLE_TX_RX_FIFO
W
1
It enables both the Tx and Rx FIFOs and is hardwired to 1,
which means it is always enabled and cannot be changed.
Table 470 •
FCR
(continued)
Bit
Number
Name
R/W
Default
State
Description
BaudRate
APB_X_CLK
16DivisorValue
------------------------------------------
=
BaudRate
APB_X_CLK
2DivisorValue
---------------------------------------
=
MaxBaudRate
APB_X_CLK
2 GlitchFilterLength
+
------------------------------------------------------------
=
FractionalBaudRate
APB_X_CLK
16 DMR DLR
DFR 64
+
+
(
)
------------------------------------------------------------------------------
=
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