Real Time Clock 252 May 03, 2004
Philips Semiconductors Preliminary User Manual
LPC2119/2129/2194/2292/2294ARM-based Microcontroller
ALARM REGISTER GROUP
The alarm registers are shown in Table 188. The values in these registers are compared with the time counters. If all the
unmasked (See “Alarm Mask” on page 247.) alarm registers match their corresponding time counters then an interrupt is
generated. The interrupt is cleared when a one is written to bit one of the Interrupt Location Register (ILR[1]).
RTC USAGE NOTES
Since the RTC operates from the VPB clock (pclk), any interruption of that clock will cause the time to drift away from the time
value it would have provided otherwise. The variance could be to actual clock time if the RTC was initialized to that, or simply an
error in elapsed time since the RTC was activated.
No provision is made in the LPC2119/2129/2194/2292/2294 to retain RTC status upon power loss, or to maintain time
incrementation if the clock source is lost, interrupted, or altered. Loss of chip power will result in complete loss of all RTC register
contents. Entry to Power Down mode will cause a lapse in the time update. Altering the RTC timebase during system operation
(by reconfiguring the PLL, the VPB timer, or the RTC prescaler) will result in some form of accumulated time error.
Table 188: Alarm Registers
Address Name Size Description Access
0xE0024060 ALSEC 6 Alarm value for Seconds R/W
0xE0024064 ALMIN 6 Alarm value for Minutes R/W
0xE0024068 ALHOUR 5 Alarm value for Hours R/W
0xE002406C ALDOM 5 Alarm value for Day of Month R/W
0xE0024070 ALDOW 3 Alarm value for Day of Week R/W
0xE0024074 ALDOY 9 Alarm value for Day of Year R/W
0xE0024078 ALMON 4 Alarm value for Months R/W
0xE002407C ALYEAR 12 Alarm value for Years R/W
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