PCF2123 Datasheet, PDF (19/54 Pages) NXP Semiconductors – SPI Real time clock/calendar

NXP Semiconductors
PCF2123
SPI Real time clock/calendar
check now signal
MINUTE ALARM
MINUTE TIME
HOUR ALARM
HOUR TIME
DAY ALARM
DAY TIME
MINUTE AEN
=
HOUR AEN
=
DAY AEN
=
example
MINUTE AEN = 1
1
0
set alarm flag, AF⁽¹⁾
WEEKDAY ALARM
WEEKDAY TIME
WEEKDAY AEN
=
001aaf902
(1) Only when all enabled alarm settings are matching.
Fig 12. Alarm function block diagram
The generation of interrupts from the alarm function is described in Section 9.9.3.
9.7.1 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 to match the alarm condition.
Alarm registers which have bit AEN_x at logic 1 are ignored.
Table 23 shows an example for clearing bit AF but leaving bit MSF and bit TF unaffected.
Clearing the flags is made 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.
PCF2123_1
Product data sheet
minutes counter 44
45
46
minute alarm 45
AF
INT when AIE = 1
001aaf903
Example where only the minute alarm is used and no other interrupts are enabled.
Fig 13. AF timing
Rev. 01 — 19 November 2008
© NXP B.V. 2008. All rights reserved.
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