Datasheet

UM10398 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2014. All rights reserved.
User manual Rev. 12.3 — 10 June 2014 23 of 547
NXP Semiconductors
UM10398
Chapter 3: LPC111x/LPC11Cxx System configuration (SYSCON)
3.4 Clock generation
See Figure 8 for an overview of the LPC111x/LPC11Cxx Clock Generation Unit (CGU).
The LPC111x/LPC11Cxx include three independent oscillators. These are the system
oscillator, the Internal RC oscillator (IRC), and the watchdog oscillator. Each oscillator can
be used for more than one purpose as required in a particular application.
Following reset, the LPC111x/LPC11Cxx will operate from the Internal RC oscillator until
switched by software. This allows systems to operate without any external crystal and the
bootloader code to operate at a known frequency.
The SYSAHBCLKCTRL register gates the system clock to the various peripherals and
memories. UART, the WDT, and SPI0/1 have individual clock dividers to derive peripheral
clocks from the main clock.
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.
For details on power control see Section 3.9
.
Table 6. Pin summary
Pin name Pin direction Pin description
CLKOUT O Clockout pin
PIO0_0 to PIO0_11 I Start logic wake-up pins port 0
PIO1_0 I Start logic wake-up pin port 1