UM10850
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User manual
Rev. 2.4 — 13 September 2016
38 of 464
NXP Semiconductors
UM10850
Chapter 4: LPC5410x System configuration (SYSCON)
4.5.16 Main clock source select register A
This register selects one of the internal oscillators, IRC, system oscillator, or watchdog
oscillator. The oscillator selected is then one of the inputs to the main clock source select
register B (see
), which selects the clock source for the main clock. All clocks to
the core, memories, and peripherals on the synchronous APB bus are derived from the
main clock.
Remark:
Note that this selection is internally synchronized: the clock being switched from
and the clock being switched to must both be running and have occurred in specific states
before the selection actually changes.
4.5.17 Main clock source select register B
This register selects the clock source for the main clock. All clocks to the core, memories,
and peripherals are derived from the main clock.
One input to this register is the main clock source select register A (see
), which
selects one of the three internal oscillators, IRC, system oscillator, or watchdog oscillator.
Remark:
Note that this selection is internally synchronized: the clock being switched from
and the clock being switched to must both be running and have occurred in specific states
before the selection actually changes.
4.5.18 ADC clock source select register
This register selects a clock source for the 12-bit ADCs that is to the system clock. To use
a clock other than the Main clock, select the asynchronous clock mode in the ADC control
register.
Table 45.
Main clock source select register A (MAINCLKSELA, address 0x4000 0080) bit
description
Bit
Symbol
Value
Description
Reset value
1:0
SEL
Clock source for main clock source selector A
0
0x0
IRC Oscillator
0x1
CLKIN
0x2
Watchdog oscillator
0x3
Reserved
31:2
-
-
Reserved
-
Table 46.
Main clock source select register B (MAINCLKSELB, address 0x4000 0084) bit
description
Bit
Symbol
Value
Description
Reset value
1:0
SEL
Clock source for main clock source selector B. Selects the
clock source for the main clock.
0
0x0
MAINCLKSELA. Use the clock source selected in
MAINCLKSELA register.
0x1
System PLL input.
0x2
System PLL output.
0x3
RTC oscillator output. RTC oscillator 32 kHz output.
31:2
-
-
Reserved
-