LPC2460_08 Datasheet, PDF (39/68 Pages) NXP Semiconductors – Flashless 16-bit/32-bit micro; Ethernet, CAN, ISP/IAP, USB 2.0 device/host/OTG, external memory interface

NXP Semiconductors
LPC2460
Fast communication chip
7.23.1 Features
• 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.
7.24 Clocking and power control
7.24.1 Crystal oscillators
The LPC2460 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 LPC2460 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.
7.24.1.1 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.
Upon power-up or any chip reset, the LPC2460 uses the IRC as the clock source.
Software may later switch to one of the other available clock sources.
7.24.1.2 Main oscillator
The main oscillator can be used as the clock source for the CPU, with or without using the
PLL. The main oscillator 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
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 7.24.2 for additional information.
LPC2460_2
Preliminary data sheet
Rev. 02 — 1 February 2008
© NXP B.V. 2008. All rights reserved.
39 of 68