Datasheet
LPC11E1X All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 1.1 — 24 September 2013 21 of 62
NXP Semiconductors
LPC11E1x
32-bit ARM Cortex-M0 microcontroller
7.16.1.1 Internal RC oscillator
The IRC can be used as the clock source for the WDT, and/or as the clock that drives the
system PLL and then the CPU. The nominal IRC frequency is 12 MHz.
Upon power-up, any chip reset, or wake-up from Deep power-down mode, the LPC11E1x
use the IRC as the clock source. Software can later switch to one of the other available
clock sources.
7.16.1.2 System oscillator
The system oscillator can be used as the clock source for the CPU, with or without using
the PLL.
The system oscillator operates at frequencies of 1 MHz to 25 MHz. This frequency can be
boosted to a higher frequency, up to the maximum CPU operating frequency, by the
system PLL.
7.16.1.3 Watchdog oscillator
The watchdog oscillator can be used as a clock source that directly drives the CPU, the
watchdog timer, or the CLKOUT pin. The watchdog oscillator nominal frequency is
programmable between 7.8 kHz and 1.7 MHz. The frequency spread over processing and
temperature is 40 % (see also Table 13
).
Fig 6. LPC11E1x clocking generation block diagram
watchdog oscillator
IRC oscillator
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
WDCLKSEL
(WDT clock select)
watchdog oscillator
IRC oscillator
system oscillator
CLKOUT PIN CLOCK
DIVIDER
CLKOUT pin
CLKOUTUEN
(CLKOUT update enable)
002aag687
system clock
SYSTEM PLL
IRC oscillator
system oscillator
watchdog oscillator
MAINCLKSEL
(main clock select)
SYSPLLCLKSEL
(system PLL clock select)
main clock
IRC oscillator
n