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M41T80M

Serial access real-time clock with alarm

STMicroelectronics 

M41T80

Clock operation

3.2

Note:

Setting alarm clock registers

Address locations 0Ah-0Eh contain the alarm settings. 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 4: Alarm repeat

modes 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.

If the address pointer is allowed to increment to the flag register address, an alarm condition

will not cause the interrupt/flag to occur until the address pointer is moved to a different

address. It should also be noted that if the last address 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 11.

A subsequent READ of the flags register is necessary to see that the value of the alarm flag

has been reset to '0.'

Figure 11. Alarm interrupt reset waveform

0Eh

0Fh

10h

ACTIVE FLAG

IRQ/OUT/SQW

Table 4.

RPT5

1

1

1

1

1

0

Alarm repeat modes

RPT4

RPT3

RPT2

1

1

1

1

1

1

1

1

0

1

0

0

0

0

0

0

0

0

RPT1

1

0

0

0

0

0

HIGH-Z

AI07021

Alarm setting

Once per second

Once per minute

Once per hour

Once per day

Once per month

Once per year

Doc ID 9074 Rev 5

15/27

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