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LPC1759_58_56_54_52_51 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 8.5 — 24 June 2014 30 of 80
NXP Semiconductors
LPC1759/58/56/54/52/51
32-bit ARM Cortex-M3 microcontroller
8.29.1.1 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.
8.29.1.2 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 8.29.2
for additional information.
8.29.1.3 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