User Manual

UM10360 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2010. All rights reserved.
User manual Rev. 2 — 19 August 2010 568 of 840
NXP Semiconductors
UM10360
Chapter 27: LPC17xx Real-Time Clock (RTC) and backup registers
27.6.6 General purpose registers
27.6.6.1 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.
27.6.7 Alarm register group
The alarm registers are shown in Table 521. 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 563) 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]).
27.7 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 retain its time value and the 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.
Table 520. 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 521. 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