lpc2377 NXP Semiconductors, lpc2377 Datasheet - Page 29

• Manufacturer Part Number: lpc2377
• Description: Single-chip 16-bit/32-bit Microcontroller; 512 Kb ?ash With Isp/iap, Ethernet, Usb 2.0, Can, And 10-bit Adc/dac
• Manufacturer: NXP Semiconductors

NXP Semiconductors
LPC2377_78_4
Product data sheet
7.25.1.1 Internal RC oscillator
7.24.1 Features
7.25.1 Crystal oscillators
7.25 Clocking and power control
based on the APB clock. Also, the RTC is powered by its own power supply pin, VBAT,
which can be connected to a battery or to the same 3.3 V supply used by the rest of the
device.
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 LPC2377/78 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 LPC2377/78 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 LPC2377/78 uses the IRC as the clock source.
Software may later switch to one of the other available clock sources.
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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 from Power-down mode, or
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.
2 kB data SRAM powered by VBAT.
RTC and battery RAM power supply is isolated from the rest of the chip.
Rev. 04 — 19 November 2008
Single-chip 16-bit/32-bit microcontroller
LPC2377/78
© NXP B.V. 2008. All rights reserved.
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