Datasheet

Clock operation M41T66
18/34 Doc ID 15108 Rev 2
3.3 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. Ta bl e 3 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, the
alarm condition activates the IRQ
/OUT. To disable the alarm, write '0' to the alarm date
register and to RPT5–RPT1.
Note: 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 output is cleared by a READ to the flags register as shown in Figure 13. A
subsequent READ of the flags register is necessary to see that the value of the alarm flag
has been reset to '0.'
Figure 13. Alarm interrupt reset waveform
Table 3. Alarm repeat modes
RPT5 RPT4 RPT3 RPT2 RPT1 Alarm setting
1 1 1 1 1 Once per second
1 1 1 1 0 Once per minute
1 1 1 0 0 Once per hour
1 1 0 0 0 Once per day
1 0 0 0 0 Once per month
0 0 0 0 0 Once per year
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