M41T80 datasheet(14/20 Pages) STMICROELECTRONICS

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M41T80

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Setting Alarm Clock Registers

Address locations 0Ah-0Eh contain the alarm set-

tings. The alarm can be configured to go off at a

prescribed time on a specific month, date, hour,

minute, or second or repeat every year, month,

day, hour, minute, or second.

Bits RPT5-RPT1 put the alarm in the repeat mode

of operation. Table 9, page 14 shows the possible

configurations. Codes not listed in the table default

to the once per second mode to quickly alert the

user of an incorrect alarm setting.

When the clock information matches the alarm

clock settings based on the match criteria defined

by RPT5-RPT1, the AF (Alarm Flag) is set. If AFE

(Alarm Flag Enable) is also set (and SQWE is '0.'),

the alarm condition activates the IRQ/OUT/SQW

pin.

Note: If the address pointer is allowed to incre-

ment to the Flag Register address, an alarm con-

dition will not cause the Interrupt/Flag to occur until

the address pointer is moved to a different ad-

dress. It should also be noted that if the last ad-

dress written is the “Alarm Seconds,” the address

pointer will increment to the Flag address, causing

this situation to occur.

The IRQ/OUT/SQW output is cleared by a READ

to the Flags Register as shown in Figure 13. A

subsequent READ of the Flags Register is neces-

sary to see that the value of the Alarm Flag has

been reset to '0.'

Figure 13. Alarm Interrupt Reset Waveform

Table 9. Alarm Repeat Modes

RPT5

RPT4

RPT3

RPT2

RPT1

Alarm Setting

Once per Second

Once per Minute

Once per Hour

Once per Day

Once per Month

Once per Year

IRQ/OUT/SQW

ACTIVE FLAG

0Fh

0Eh

10h

HIGH-Z

AI07021

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