UM10462
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© NXP B.V. 2016. All rights reserved.
User manual
Rev. 5.5 — 21 December 2016
20 of 523
NXP Semiconductors
UM10462
Chapter 3: LPC11U3x/2x/1x System control block
The main clock, and the clock outputs from the IRC, the system oscillator, and the
watchdog oscillator can be observed directly on the CLKOUT pin.
3.5 Register description
All system control block registers are on word address boundaries. Details of the registers
appear in the description of each function.
Fig 7.
LPC11U3x/2x/1x CGU block diagram
system oscillator
watchdog oscillator
IRC oscillator
USB PLL
USBPLLCLKSEL
(USB clock select)
SYSTEM CLOCK
DIVIDER
SYSAHBCLKCTRLn
(AHB clock enable)
CPU, system control,
PMU
memories,
peripheral clocks
SSP0 PERIPHERAL
CLOCK DIVIDER
SSP0
SSP1 PERIPHERAL
CLOCK DIVIDER
SSP1
USART PERIPHERAL
CLOCK DIVIDER
UART
WDT
CLKSEL
(WDT clock select)
USB 48 MHz CLOCK
DIVIDER
USB
USBUEN
(USB clock update enable)
watchdog oscillator
IRC oscillator
system oscillator
CLKOUT PIN CLOCK
DIVIDER
CLKOUT pin
CLKOUTUEN
(CLKOUT update enable)
002aaf892
system clock
SYSTEM PLL
IRC oscillator
system oscillator
IRC oscillator
watchdog oscillator
MAINCLKSEL
(main clock select)
SYSPLLCLKSEL
(system PLL clock select)
main clock
IRC oscillator
n