lpc2420 NXP Semiconductors, lpc2420 Datasheet - Page 39

• Manufacturer Part Number: lpc2420
• Description: Flashless 16-bit/32-bit Microcontroller; Ethernet, Can, Isp/iap, Usb 2.0 Device/host/otg, External Memory Interface
• Manufacturer: NXP Semiconductors

NXP Semiconductors
LPC2420_60_3
Preliminary data sheet
7.24.1.1 Internal RC oscillator
7.24.1.2 Main oscillator
7.23.1 Features
7.24.1 Crystal oscillators
7.24 Clocking and power control
The VBAT pin supplies power only to the RTC and the Battery RAM. These two functions
require a minimum of power to operate, which can be supplied by an external battery.
When the CPU and the rest of chip functions are stopped and power removed, the RTC
can supply an alarm output that can be used by external hardware to restore chip power
and resume operation.
The LPC2420/2460 includes three independent oscillators. These are the Main Oscillator,
the Internal RC oscillator, and the RTC oscillator. Each oscillator can be used for more
than one purpose as required in a particular application. Any of the three clock sources
can be chosen by software to drive the PLL and ultimately the CPU.
Following reset, the LPC2420/2460 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 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.
Upon power-up or any chip reset, the LPC2420/2460 uses the IRC as the clock source.
Software may later switch to one of the other available clock sources.
The main oscillator can be used as the clock source for the CPU, with or without using the
PLL. The main oscillator operates at frequencies of 1 MHz to 24 MHz. This frequency can
be boosted to a higher frequency, up to the maximum CPU operating frequency, by the
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
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Measures the passage of time to maintain a calendar and clock.
Ultra low power design to support battery powered systems.
Provides Seconds, Minutes, Hours, Day of Month, Month, Year, Day of Week, and Day
of Year.
Dedicated 32 kHz oscillator or programmable prescaler from APB clock.
Dedicated power supply pin can be connected to a battery or to the main 3.3 V.
An alarm output pin is included to assist in waking up when the chip has had power
removed to all functions except the RTC and Battery RAM.
Periodic interrupts can be generated from increments of any field of the time registers,
and selected fractional second values. This enhancement enables the RTC to be
used as a System Timer.
2 kB data SRAM powered by VBAT.
RTC and Battery RAM power supply is isolated from the rest of the chip.
Rev. 03 — 20 November 2008
Flashless 16-bit/32-bit microcontroller
LPC2420/2460
© NXP B.V. 2008. All rights reserved.
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