
UM10237_2
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 02 — 19 December 2008
653 of 792
NXP Semiconductors
UM10237
Chapter 26: LPC24XX Real-Time Clock (RTC) and battery RAM
6.2.6 Alarm Mask Register (AMR - 0xE002 4010)
The Alarm Mask Register (AMR) allows the user to mask any of the alarm registers.
shows the relationship between the bits in the AMR and the alarms. For the
alarm function, every non-masked alarm register must match the corresponding time
counter for an interrupt to be generated. The interrupt is generated only when the counter
comparison first changes from no match to match. The interrupt is removed when a one is
written to the appropriate bit of the Interrupt Location Register (ILR). If all mask bits are
set, then the alarm is disabled.
Table 572. Counter Increment Select Mask register (CISS - address 0xE002 4040) bit description
Bit Symbol
Value Description
Reset
value
2:0 SubSecSel
SubSecSelSub-Second Select. This field selects a count for the sub-second interrupt as
follows:
NC
000
An interrupt is generated on every 16 counts of the Clock Tick Counter. At 32.768 kHz,
this generates an interrupt approximately every 488 microseconds.
001
An interrupt is generated on every 32 counts of the Clock Tick Counter. At 32.768 kHz,
this generates an interrupt approximately every 977 microseconds.
010
An interrupt is generated on every 64 counts of the Clock Tick Counter. At 32.768 kHz,
this generates an interrupt approximately every 1.95 milliseconds.
011
An interrupt is generated on every 128 counts of the Clock Tick Counter. At 32.768 kHz,
this generates an interrupt approximately every 3.9 milliseconds.
100
An interrupt is generated on every 256 counts of the Clock Tick Counter. At 32.768 kHz,
this generates an interrupt approximately every 7.8 milliseconds.
101
An interrupt is generated on every 512 counts of the Clock Tick Counter. At 32.768 kHz,
this generates an interrupt approximately every 15.6 milliseconds.
110
An interrupt is generated on every 1024 counts of the Clock Tick Counter. At 32.768 kHz,
this generates an interrupt approximately every 31.25 milliseconds.
111
An interrupt is generated on every 2048 counts of the Clock Tick Counter. At 32.768 kHz,
this generates an interrupt approximately every 62.5 milliseconds.
6:3 Unused
Reserved, user software should not write ones to reserved bits. The value read from a
reserved bit is not defined.
NA
7
SubSecEna
Subsecond interrupt enable.
NC
0
The sub-second interrupt is disabled.
1
The sub-second interrupt is enabled.
Table 573. Alarm Mask Register (AMR - address 0xE002 4010) bit description
Bit
Symbol
Description
Reset
value
0
AMRSEC
When 1, the Second value is not compared for the alarm.
NA
1
AMRMIN
When 1, the Minutes value is not compared for the alarm.
NA
2
AMRHOUR When 1, the Hour value is not compared for the alarm.
NA
3
AMRDOM
When 1, the Day of Month value is not compared for the alarm.
NA
4
AMRDOW
When 1, the Day of Week value is not compared for the alarm.
NA
5
AMRDOY
When 1, the Day of Year value is not compared for the alarm.
NA
6
AMRMON
When 1, the Month value is not compared for the alarm.
NA
7
AMRYEAR
When 1, the Year value is not compared for the alarm.
NA