UM10360 Datasheet, PDF (565/835 Pages) NXP Semiconductors – LPC17xx User manual

NXP Semiconductors
UM10360
Chapter 27: LPC17xx Real-Time Clock (RTC) and backup registers
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.
Table 521. 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
6.7 Alarm register group
The alarm registers are shown in Table 27–522. The values in these registers are
compared with the time counters. If all the unmasked (See Section 27–6.2.4 “Alarm Mask
Register (AMR - 0x4002 4010)” on page 560) 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]).
Table 522. Alarm registers
Name
Size Description
ALSEC 6
Alarm value for Seconds
ALMIN
6
Alarm value for Minutes
ALHOUR 5
Alarm value for Hours
ALDOM 5
Alarm value for Day of Month
ALDOW 3
Alarm value for Day of Week
ALDOY 9
Alarm value for Day of Year
ALMON 4
Alarm value for Months
ALYEAR 12 Alarm value for Years
Access
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Address
0x4002 4060
0x4002 4064
0x4002 4068
0x4002 406C
0x4002 4070
0x4002 4074
0x4002 4078
0x4002 407C
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. As long as power is
available on either V_DD(REG)(3V3) or V_BAT, the RTC will lose its time value and backup
register contents. If both V_DD(REG)(3V3) and V_BAT are not present, all RTC information will
be lost. RTC incrementation will stop or be unpredictable if the clock source is lost,
interrupted, or altered.
UM10360_1
User manual
Rev. 01 — 4 January 2010
© NXP B.V. 2010. All rights reserved.
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