PCF2129AT datasheet(26/68 Pages) NXP

26 / 68 page

PCF2129A_1

Product data sheet

Rev. 01 — 13 January 2010

26 of 68

NXP Semiconductors

PCF2129A

Integrated RTC, TCXO and quartz crystal

As an example, if the time (seconds through to hours) is set in one access and then in a

second access the date is set, it is possible that the time may increment between the two

accesses. A similar problem exists when reading. A roll over may occur between reads

thus giving the minutes from one moment and the hours from the next. Therefore it is

advised to read all time and date registers in one access.

8.9 Alarm function

When one or more of the alarm bit fields are loaded with a valid second, minute, hour, day,

or weekday and its corresponding alarm enable bit (AE_x) is logic 0, then that information

is compared with the actual second, minute, hour, day, and weekday (see Figure 15).

The generation of interrupts from the alarm function is described in Section 8.12.4.

(1) Only when all enabled alarm settings are matching.

Fig 15. Alarm function block diagram

013aaa236

WEEKDAY ALARM

AE_W

WEEKDAY TIME

DAY ALARM

AE_D

DAY TIME

HOUR ALARM

AE_H

HOUR TIME

MINUTE ALARM

check now signal

set alarm flag AF (1)

AE_S = 1

example

AE_M

MINUTE TIME

SECOND TIME

SECOND ALARM

AE_S

PCF2129AT Datasheet(PDF) 26 Page - NXP Semiconductors