Datasheet

LPC122X All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
Product data sheet Rev. 2 — 26 August 2011 24 of 61
NXP Semiconductors
LPC122x
32-bit ARM Cortex-M0 microcontroller
7.18.1.1 Internal RC oscillator
The IRC may be used as the clock source for the WDT, and/or as the clock that drives the
PLL and subsequently the CPU. The nominal IRC frequency is 12 MHz. The IRC is
trimmed to 1 % accuracy over the entire voltage and temperature range.
Upon power-up or any chip reset, the LPC122x use the IRC as the clock source. Software
may later switch to one of the other available clock sources.
7.18.1.2 System oscillator
The system oscillator can be used as the clock source for the CPU, with or without using
the PLL.
Fig 5. LPC122x clocking generation block diagram
SYSTEM PLL
watchdog oscillator
IRC oscillator
IRC oscillator
IRC oscillator
watchdog oscillator
system oscillator
MAINCLKSEL
(main clock select)
SYSPLLCLKSEL
CLOCK
DIVIDER
AHB clock 0
(system)
CLOCK
DIVIDER
peripheral clocks
(SSP, UART0, UART1)
RTC
WWDT
watchdog oscillator
IRC oscillator
system oscillator
CLOCK
DIVIDER
CLKOUT pin
CLKOUTUEN
(CLKOUT clock update enable)
RTC oscillator 1 kHz clock
RTC oscillator 1 Hz clock
RTC oscillator 1 Hz delayed clock
RTCOSCCTRL
WDCLKSEL
(WWDT clock select)
main clock system clock
3
CLOCK
DIVIDER
SYSAHBCLKCTRL[1:31]
(AHB clock enable)
AHB clocks
1 to 31
(memories
and peripherals)
31
002aaf271
CLOCK
DIVIDER
peripheral clocks
(IOCONFIG glitch filter)
7