UM10850
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© NXP B.V. 2016. All rights reserved.
User manual
Rev. 2.4 — 13 September 2016
66 of 464
NXP Semiconductors
UM10850
Chapter 4: LPC5410x System configuration (SYSCON)
4.5.59 Asynchronous APB clock divider register
This register controls how the asynchronous APB clock is divided before use by
peripherals. The clock can be shut down completely by setting the DIV field to zero.
4.5.60 USART fractional baud rate generator register
All USART peripherals share a common clock (see
), which can be adjusted by a
fractional divider. This register sets the MULT and DIV values for the fractional rate
generator. The output rate is:
USART clock = async bridge clock rate / (1 + MULT / DIV
The async bridge clock rate is the USART clock configured as selected via
ASYNCAPBCLKSELA (
), and
divided as defined by the ASYNCCLKDIV register (
Remark:
In order to use the fractional baud rate generator, 0xFF must first be written to
the DIV value to yield a denominator value of 256. All other values are not supported.
Section 21.3.1 “Configure the USART clock and baud rate”
Table 97.
Asynchronous clock source select register B (ASYNCAPBCLKSELB, address
0x4008 0024) bit description
Bit
Symbol
Value
Description
Reset value
1:0
SEL
Clock source for asynchronous clock source selector B.
0
0x0
Main clock
0x1
CLKIN
0x2
System PLL output.
0x3
ASYNCAPBCLKSELA. Clock selected by the
ASYNCAPBCLKSELA register.
31:2
-
-
Reserved
-
Table 98.
Asynchronous APB clock divider register (ASYNCCLKDIV, address 0x4008 0028)
bit description
Bit
Symbol
Description
Reset value
7:0
DIV
Asynchronous APB clock divider value.
0: Clock disabled.
1: Divide by 1.
to
255: Divide by 255.
0x01
31:8
-
Reserved
-
Table 99.
USART fractional baud rate generator register (FRGCTRL, address 0x4008 0030) bit description
Bit
Symbol
Description
Reset value
7:0
DIV
Denominator of the fractional divider. DIV is equal to the programmed value +1. Always set
to 0xFF to use with the fractional baud rate generator.
0xFF
15:8
MULT
Numerator of the fractional divider. MULT is equal to the programmed value.
0
31:16
-
Reserved
-