PCF2123 datasheet(18/63 Pages) NXP

18 / 63 page

PCF2123

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Product data sheet

Rev. 5 — 27 April 2011

18 of 63

NXP Semiconductors

PCF2123

SPI Real time clock/calendar

8.5.4 Register Weekday_alarm

[1]

Default value.

8.5.5 Alarm flag

By clearing the MSB, AE_x (Alarm Enable), of one or more of the alarm registers the

corresponding alarm condition(s) are active. When an alarm occurs, AF (register

Control_2, see Table 7) is set logic 1. The asserted AF can be used to generate an

interrupt (INT). The AF is cleared using the interface.

The registers at addresses 09h through 0Ch contain alarm information. When one or

more of these registers is loaded with minute, hour, day, or weekday, and its

corresponding Alarm Enable bit (AE_x) is logic 0, then that information is compared with

the current minute, hour, day, and weekday. When all enabled comparisons first match,

the Alarm Flag (AF) is set logic 1.

Table 21.

Weekday_alarm - weekday alarm register (address 0Ch) bit description

Bit

Symbol

Value

Description

AE_W

weekday alarm is enabled

1[1]

weekday alarm is disabled

6 to 3

unused

2 to 0

WEEKDAY_ALARM

0 to 6

weekday alarm information coded in BCD

format

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

It’s only on increment to a matched case that the alarm flag is set, see Section 8.5.5.

Fig 12. Alarm function block diagram

013aaa088

WEEKDAY ALARM

AE_W

WEEKDAY TIME

DAY ALARM

AE_D

DAY TIME

HOUR ALARM

AE_H

HOUR TIME

MINUTE ALARM

AE_M

MINUTE TIME

check now signal

set alarm flag AF (1)

AE_M = 1

example

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