48GA004 datasheet(186/268 Pages) MICROCHIP

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PIC24FJ64GA004 FAMILY

DS39881D-page 186

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19.3

Alarm

• Configurable from half second to one year

• Enabled using the ALRMEN bit

(ALCFGRPT<15>, Register 19-3)

• One-time alarm and repeat alarm options

available

19.3.1

CONFIGURING THE ALARM

The alarm feature is enabled using the ALRMEN bit.

This bit is cleared when an alarm is issued. Writes to

ALRMVAL should only take place when ALRMEN = 0.

As shown in Figure 19-2, the interval selection of the

alarm is configured through the AMASK bits

(ALCFGRPT<13:10>). These bits determine which and

how many digits of the alarm must match the clock

value for the alarm to occur.

The alarm can also be configured to repeat based on a

preconfigured interval. The amount of times this occurs

once the alarm is enabled is stored in the ARPT bits,

ARPT7:ARPT0 (ALCFGRPT<7:0>). When the value of

the ARPT bits equals 00h and the CHIME bit

(ALCFGRPT<14>) is cleared, the repeat function is

disabled and only a single alarm will occur. The alarm

can be repeated up to 255 times by loading

ARPT7:ARPT0 with FFh.

After each alarm is issued, the value of the ARPT bits

is decremented by one. Once the value has reached

00h, the alarm will be issued one last time, after which

the ALRMEN bit will be cleared automatically and the

alarm will turn off.

Indefinite repetition of the alarm can occur if the CHIME

bit = 1. Instead of the alarm being disabled when the

value of the ARPT bits reaches 00h, it rolls over to FFh

and continues counting indefinitely while CHIME is set.

19.3.2

ALARM INTERRUPT

At every alarm event, an interrupt is generated. In addi-

tion, an alarm pulse output is provided that operates at

half the frequency of the alarm. This output is

completely synchronous to the RTCC clock and can be

used as a trigger clock to other peripherals.

FIGURE 19-2:

ALARM MASK SETTINGS

Note:

Changing any of the registers, other then

the RCFGCAL and ALCFGRPT registers

and the CHIME bit while the alarm is

enabled (ALRMEN = 1), can result in a

false alarm event leading to a false alarm

interrupt. To avoid a false alarm event, the

timer and alarm values should only be

changed while the alarm is disabled

(ALRMEN = 0). It is recommended that the

ALCFGRPT register and CHIME bit be

changed when RTCSYNC = 0.

Note

Annually, except when configured for February 29.

Day of

the

Week

Month

Day

Hours

Minutes

Seconds

Alarm Mask Setting

(AMASK3:AMASK0)

0000

– Every half second

0001

– Every second

0010

– Every 10 seconds

0011

– Every minute

0100

– Every 10 minutes

0101

– Every hour

0110

– Every day

0111

– Every week

1000

– Every month

1001

– Every year(1)

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