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UM10237_2
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 02 — 19 December 2008
660 of 792
NXP Semiconductors
UM10237
Chapter 26: LPC24XX Real-Time Clock (RTC) and battery RAM
11. Battery RAM
The Battery RAM is a 2 kbyte static RAM residing on the APB bus. The address range is
0xE008 4000 to 0xE008 47FF.The SRAM can be accessed word-wise (32-bit) only.
The Battery RAM is powered from the VBAT pin along with the RTC, both of which exist
in a power domain that is isolated from the rest of the chip. This allows them to operate
while the main chip power has been removed.
12. RTC external 32 kHz oscillator component selection
The RTC external oscillator circuit is shown in
. Since the feedback
resistance is integrated on chip, only a crystal, the capacitances C
X1
and C
X2
need to be
connected externally to the microcontroller.
Table 583. Prescaler cases where the Integer Counter reload value is incremented
Fraction Counter
PREFRAC Bit
14 13 12 11 10 9
8
7
6
5
4
3
2
1
0
--- ---- ---- ---1
1
-
-
-
-
-
-
-
-
-
-
-
-
-
-
--- ---- ---- --10
-
1
-
-
-
-
-
-
-
-
-
-
-
-
-
--- ---- ---- -100
-
-
1
-
-
-
-
-
-
-
-
-
-
-
-
--- ---- ---- 1000
-
-
-
1
-
-
-
-
-
-
-
-
-
-
-
--- ---- ---1 0000
-
-
-
-
1
-
-
-
-
-
-
-
-
-
-
--- ---- --10 0000
-
-
-
-
-
1
-
-
-
-
-
-
-
-
-
--- ---- -100 0000
-
-
-
-
-
-
1
-
-
-
-
-
-
-
-
--- ---- 1000 0000
-
-
-
-
-
-
-
1
-
-
-
-
-
-
-
--- ---1 0000 0000
-
-
-
-
-
-
-
-
1
-
-
-
-
-
-
--- --10 0000 0000
-
-
-
-
-
-
-
-
-
1
-
-
-
-
-
--- -100 0000 0000
-
-
-
-
-
-
-
-
-
-
1
-
-
-
-
--- 1000 0000 0000
-
-
-
-
-
-
-
-
-
-
-
1
-
-
-
--1 0000 0000 0000
-
-
-
-
-
-
-
-
-
-
-
-
1
-
-
-10 0000 0000 0000
-
-
-
-
-
-
-
-
-
-
-
-
-
1
-
100 0000 0000 0000
-
-
-
-
-
-
-
-
-
-
-
-
-
-
1