PCF2123BS NXP [NXP Semiconductors], PCF2123BS Datasheet - Page 19

• Manufacturer Part Number: PCF2123BS
• Description: SPI Real time clock/calendar
• Manufacturer: NXP [NXP Semiconductors]

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