UM10208_2
© NXP B.V. 2007. All rights reserved.
User manual
Rev. 02 — 1 June 2007
145 of 362
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, V
DD(OSC321V8)
, can be connected to a 1.8V supply from a
battery or the 1.8 V used by other parts of the device.
•
An alarm output pin is included to assist in waking up from Deep 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.
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 either mode.
3.
Architecture
4.
RTC usage notes
On the LPC288x, the clock for the RTC is created by the Clock Generation Unit (CGU).
The PWR_UP signal shown in the preceding Figure enables use of the RTC, and is
controlled by the RTC Configuration Register as described in
.
5.
RTC interrupts
Interrupt generation is controlled through the Interrupt Location Register (ILR), the
Counter Increment Interrupt Register (CIIR), the alarm registers, and the Alarm Mask
Register (AMR). Interrupts are generated only by the transition into the interrupt state. The
ILR separately enables CIIR and AMR interrupts. Each bit in the CIIR corresponds to one
of the time counters. If the CIIR bit for a particular counter is 1, then every time the counter
is incremented an interrupt is generated. The alarm registers allow the user to specify a
UM10208
Chapter 13: Real-Time Clock (RTC)
Rev. 02 — 1 June 2007
User manual
Fig 20. RTC inputs and outputs
RTC
clk32kHz
PWR_UP
APB
NINTR
ALARM_LP