LPC1102 datasheet(12/39 Pages) NXP

12 / 39 page

LPC1102

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Product data sheet

Rev. 4 — 24 June 2011

12 of 39

NXP Semiconductors

LPC1102

32-bit ARM Cortex-M0 microcontroller

7.14.1.1

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 LPC1102 uses the IRC as the clock source.

Software may later switch to one of the other available clock sources.

7.14.1.2

Watchdog oscillator

The watchdog oscillator can be used as a clock source that directly drives the CPU or the

watchdog timer. The watchdog oscillator nominal frequency is programmable between 7.8

kHz and 1.7 MHz. The frequency spread over processing and temperature is

40 %.

7.14.2 System PLL

The PLL accepts an input clock frequency in the range of 10 MHz to 25 MHz. The input

frequency is multiplied up to a high frequency with a Current Controlled Oscillator (CCO).

The multiplier can be an integer value from 1 to 32. The CCO operates in the range of

156 MHz to 320 MHz, so there is an additional divider in the loop to keep the CCO within

its frequency range while the PLL is providing the desired output frequency. The PLL

output frequency must be lower than 100 MHz. The output divider may be set to divide by

2, 4, 8, or 16 to produce the output clock. Since the minimum output divider value is 2, it is

insured that the PLL output has a 50 % duty cycle. The PLL is turned off and bypassed

Fig 4.

LPC1102 clock generation block diagram

SYSTEM PLL

IRC oscillator

external clock

watchdog oscillator

IRC oscillator

watchdog oscillator

MAINCLKSEL

(main clock select)

SYSPLLCLKSEL

(system PLL clock select)

SYSTEM CLOCK

DIVIDER

AHB clock 0

(system)

AHBCLKCTRL[1:18]

(AHB clock enable)

AHB clocks 1 to 18

(memories

and peripherals)

SPI0 PERIPHERAL

CLOCK DIVIDER

SPI0

UART PERIPHERAL

CLOCK DIVIDER

UART

WDT CLOCK

DIVIDER

WDT

WDTUEN

(WDT clock update enable)

002aaf527

main clock

system clock

IRC oscillator

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