UM10237_2 © NXP B.V. 2008. All rights reserved.
User manual Rev. 02 — 19 December 2008 648 o f 792
NXP Semiconductors UM10237
Chapter 26: LPC24XX Real-Time Clock (RTC) and battery RAM

and resume operation. The alarm output has a nominal voltage swing of 1.8 V. Note that

the PLL is disabled when waking up from power down. See Section4–3.2.10 for the PLL

start-up procedure.

4. Architecture
5. Pin description
Fig 134. RTC block diagram
CCLK
INTERRUPT GENERATOR
COUNTER INCREMENT
INTERRUPT ENABLE
ALARM MASK
REGISTER
counter
enables
CLK1
REFERENCE CLOCK DIVIDER
(PRESCALER)
CLK32k
strobe
COMPARATORS
CLOCK GENERATOR
ALARM
REGISTERS
TIME COUNTERS
RTC OSCILLATOR
MUX
Table 565. RT C pi n de scription
Name Type Description
ALARM O Alarm output (see Section 26–8).
RTCX1 I Input to the RTC oscillator circuit.
RTCX2 O Output from the RTC oscillator circuit.
Remark: If the RTC is not used, the RTCX1/2 pins can be left
floating.
VBAT I RTC power supply: 3.3 V on this pin supplies the power to the
RTC.
Remark: If the RTC is used, VBAT must be connected to either pin
VDD(3V3) or an independent power supply (external battery).
Otherwise, VBAT should be left floating.