LPC1759 datasheet(29/64 Pages) NXP

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LPC1759_58_56_54_52_51_4

Product data sheet

Rev. 04 — 26 January 2010

29 of 64

NXP Semiconductors

LPC1759/58/56/54/52/51

32-bit ARM Cortex-M3 microcontroller

7.29.1.1

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 4 MHz. The IRC is

trimmed to 1 % accuracy over the entire voltage and temperature range.

Upon power-up or any chip reset, the LPC1759/58/56/54/52/51 use the IRC as the clock

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

7.29.1.2

Main oscillator

The main oscillator can be used as the clock source for the CPU, with or without using the

PLL. The main oscillator also provides the clock source for the dedicated USB PLL.

The main 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 main

PLL. The clock selected as the PLL input is PLLCLKIN. The ARM processor clock

frequency is referred to as CCLK elsewhere in this document. The frequencies of

PLLCLKIN and CCLK are the same value unless the PLL is active and connected. The

clock frequency for each peripheral can be selected individually and is referred to as

PCLK. Refer to Section 7.29.2 for additional information.

7.29.1.3

RTC oscillator

The RTC oscillator can be used as the clock source for the RTC block, the main PLL,

and/or the CPU.

Fig 4.

LPC1759/58/56/54/52/51 clocking generation block diagram

MAIN

OSCILLATOR

INTERNAL

OSCILLATOR

RTC

OSCILLATOR

MAIN PLL

WATCHDOG

TIMER

REAL-TIME

CLOCK

CPU

CLOCK

DIVIDER

PERIPHERAL

CLOCK

GENERATOR

USB BLOCK

ARM

CORTEX-M3

ETHERNET

BLOCK

DMA

GPIO

NVIC

USB

CLOCK

DIVIDER

system

clock

select

(CLKSRCSEL)

USB clock config

(USBCLKCFG)

CPU clock config

(CCLKCFG)

pllclk

CCLK/8

CCLK/6

CCLK/4

CCLK/2

CCLK

pclkWDT

rtclk = 1Hz

usbclk

(48 MHz)

cclk

USB PLL

USB PLL enable

main PLL enable

32 kHz

APB peripherals

LPC17xx

002aad947

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