M41T80_11 Datasheet, PDF (15/27 Pages) STMicroelectronics – Serial access real-time clock with alarm

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