Nxp Semiconductors UM10237 用户手册
UM10237_2
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 02 — 19 December 2008
647 of 792
1.
Basic configuration
The RTC is configured using the following registers:
1. Power: In the PCONP register (
), set bits PCRTC.
Remark: On reset, the RTC is enabled. See
for power saving options.
2. Clock: Select clock source in
. If the peripheral clock is selected, select
PCLK_RTC in the PCLK_SEL0 register (
). For the RTC, the peripheral
clock must be scaled (see
).
3. Interrupts: See
for RTC interrupt handling. Interrupts are enabled in
the VIC using the VICIntEnable register (
2.
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.
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.
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.
and selected fractional second values.
•
2 kilobyte static RAM powered by VBAT.
•
RTC and Battery RAM power supply is isolated from the rest of the chip.
3.
Description
The Real-Time Clock (RTC) is a set of counters for measuring time when system power is
on, and optionally when it is off. It uses little power in power down mode. On the
LPC2400, the RTC can be clocked by a separate 32.768 KHz oscillator or by a
programmable prescale divider based on the APB clock. 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.
on, and optionally when it is off. It uses little power in power down mode. On the
LPC2400, the RTC can be clocked by a separate 32.768 KHz oscillator or by a
programmable prescale divider based on the APB clock. 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
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
UM10237
Chapter 26: LPC24XX Real-Time Clock (RTC) and battery RAM
Rev. 02 — 19 December 2008
User manual