PCA2125 datasheet(12/36 Pages) NXP

12 / 36 page

PCA2125_1

Product data sheet

Rev. 01 — 28 July 2008

12 of 36

NXP Semiconductors

PCA2125

SPI Real-time clock/calendar

Generation of interrupts from the alarm function is described in Section 8.7.3.

8.5.1 Alarm ﬂag

When all enabled comparisons ﬁrst match, the alarm ﬂag bit AF is set. Bit AF will remain

set until cleared by software. Once bit AF has been cleared it will only be set again when

the time increments once more to match the alarm condition.

Alarm registers which have their bit AENx at logic 1 are ignored.

Figure 8 shows an example for clearing bit AF, but leaving bit MSF and bit TF unaffected.

The ﬂags are cleared by a write command, therefore bits 7, 6, 4, 1 and 0 must be written

with their previous values. Repeatedly re-writing these bits has no inﬂuence on the

functional behavior.

Fig 7.

Alarm function block diagram

001aaf902

WEEKDAY ALARM

WEEKDAY AEN

WEEKDAY TIME

DAY ALARM

DAY AEN

DAY TIME

HOUR ALARM

HOUR AEN

HOUR TIME

MINUTE ALARM

MINUTE AEN

MINUTE TIME

check now signal

set alarm flag, AF

MINUTE AEN = 1

example

Example where only the minute alarm is used and no other interrupts are enabled.

Fig 8.

Alarm ﬂag timing

001aaf903

minute alarm

minutes counter

INT when AIE = 1

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