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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
542 of 808
NXP Semiconductors
UM10360
Chapter 27: LPC17xx Real-Time Clock (RTC) and backup registers
•
When the calibration counter reaches CALVAL, a calibration match occurs and the
RTC timers are incremented by 2.
•
When the calibration event occurs, the LSB of the ALSEC register is forced to be one
so that the alarm interrupt will not be missed when skipping a second.
6.6 General purpose registers
6.6.1 General purpose registers 0 to 4 (GPREG0 to GPREG4 - addresses
0x4002 4044 to 0x4002 4054)
These registers can be used to store important information when the main power supply is
off. The value in these registers is not affected by chip reset.
6.7 Alarm register group
The alarm registers are shown in
. The values in these registers are
compared with the time counters. If all the unmasked (See
Register (AMR - 0x4002 4010)” on page 537
) alarm registers match their corresponding
time counters then an interrupt is generated. The interrupt is cleared when a 1 is written to
bit 1 of the Interrupt Location Register (ILR[1]).
7.
RTC usage notes
If the RTC is used, V
BAT
may be connected to an independent power supply (typically an
external battery), or left floating. The RTC domain will always be internally powered if
V
DD(REG)(3V3)
is present, even if there is no power applied to V
BAT
. If power is not available
on either V
DD(REG)(3V3)
or V
BAT
, the RTC will lose its time value and backup register
contents. RTC incrementation will stop or be unpredictable if the clock source is lost,
interrupted, or altered.
Table 502. General purpose registers 0 to 4 (GPREG0 to GPREG4 - addresses 0x4002 4044
to 0x4002 4054) bit description
Bit
Symbol
Description
Reset
value
31:0
GP0 to GP4
General purpose storage.
N/A
Table 503. Alarm registers
Name
Size
Description
Access
Address
ALSEC
6
Alarm value for Seconds
R/W
0x4002 4060
ALMIN
6
Alarm value for Minutes
R/W
0x4002 4064
ALHOUR
5
Alarm value for Hours
R/W
0x4002 4068
ALDOM
5
Alarm value for Day of Month
R/W
0x4002 406C
ALDOW
3
Alarm value for Day of Week
R/W
0x4002 4070
ALDOY
9
Alarm value for Day of Year
R/W
0x4002 4074
ALMON
4
Alarm value for Months
R/W
0x4002 4078
ALYEAR
12
Alarm value for Years
R/W
0x4002 407C