Alarm Register Group; Rtc Usage Notes - Philips LPC2194 User Manual

Philips Semiconductors
ARM-based Microcontroller

ALARM REGISTER GROUP

The alarm registers are shown in Table
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]).
Table 188: Alarm Registers
Address Name
0xE0024060 ALSEC
0xE0024064 ALMIN
0xE0024068 ALHOUR
0xE002406C ALDOM
0xE0024070 ALDOW
0xE0024074 ALDOY
0xE0024078 ALMON
0xE002407C ALYEAR

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.
Real Time Clock
188. The values in these registers are compared with the time counters. If all the
Size
6 Alarm value for Seconds
6 Alarm value for Minutes
5 Alarm value for Hours
5 Alarm value for Day of Month
3 Alarm value for Day of Week
9 Alarm value for Day of Year
4 Alarm value for Months
12 Alarm value for Years
252
LPC2119/2129/2194/2292/2294
Description
Preliminary User Manual
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May 03, 2004