lpc1778 NXP Semiconductors, lpc1778 Datasheet - Page 65

• Manufacturer Part Number: lpc1778
• Description: 32-bit Arm Cortex-m3 Microcontroller; Up To 512 Kb Flash And 96 Kb Sram; Usb Device/host/otg; Ethernet; Lcd; Emc
• Manufacturer: NXP Semiconductors

NXP Semiconductors
LPC178x_7x
Objective data sheet
7.32.1.3 RTC oscillator
7.32.2 Main PLL (PLL0)
7.32.3 PLL1
7.32.4 Wake-up timer
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
The RTC oscillator can be used as the clock source for the RTC block, the main PLL,
and/or the CPU.
The PLL0 accepts an input clock frequency in the range of 32 kHz to 25 MHz. The input
frequency is multiplied up to a high frequency, then divided down to provide the actual
clock used by the CPU.
The PLL0 input, in the range of 32 kHz to 25 MHz, may initially be divided down by a
value ‘N’, which may be in the range of 1 to 256. This input division provides a wide range
of output frequencies from the same input frequency.
Following the PLL0 input divider is the PLL0 multiplier. This can multiply the input divider
output through the use of a Current Controlled Oscillator (CCO) by a value ‘M’, in the
range of 1 through 32768. The resulting frequency must be in the range of 275 MHz to
550 MHz. The multiplier works by dividing the CCO output by the value of M, then using a
phase-frequency detector to compare the divided CCO output to the multiplier input. The
error value is used to adjust the CCO frequency.
The PLL0 is turned off and bypassed following a chip Reset and by entering Power-down
mode. PLL0 is enabled by software only. The program must configure and activate the
PLL0, wait for the PLL0 to lock, and then connect to the PLL0 as a clock source.
The LPC178x/7x contain a second PLL1 to provide clocking for the USB.
The PLL1 receives its clock input from the main oscillator only.
The PLL1 accepts an input clock frequency in the range of 10 MHz to 25 MHz. The input
frequency is multiplied up the range of <tbd> MHz for the USB clock using a Current
Controlled Oscillators (CCO). It is insured that the PLL1 output has a 50 % duty cycle.
The LPC178x/7x begin operation at power-up and when awakened from Power-down
mode by using the 12 MHz IRC oscillator as the clock source. This allows chip operation
to resume quickly. If the main oscillator or the PLL is needed by the application, software
will need to enable these features and wait for them to stabilize before they are used as a
clock source.
When the main oscillator is initially activated, the wake-up timer allows software to ensure
that the main oscillator is fully functional before the processor uses it as a clock source
and starts to execute instructions. This is important at power on, all types of Reset, and
All information provided in this document is subject to legal disclaimers.
Section 7.32.2
Rev. 00.04 — 8 July 2010
for additional information.
32-bit ARM Cortex-M3 microcontroller
LPC178x/7x
© NXP B.V. 2010. All rights reserved.
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