m41t80 STMicroelectronics, m41t80 Datasheet - Page 15

• Manufacturer Part Number: m41t80
• Description: Serial Access Real Time Clock With Alarm
• Manufacturer: STMicroelectronics

M41T80
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.
modes
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
Figure
the Alarm Flag has been reset to '0.'
Figure 11. Alarm interrupt reset waveform
Table 4.
IRQ/OUT/SQW
ACTIVE FLAG
RPT5
1
1
1
1
1
0
11. A subsequent READ of the Flags Register is necessary to see that the value of
shows the possible configurations. Codes not listed in the table default to the once
Alarm repeat modes
RPT4
1
1
1
1
0
0
0Eh
RPT3
1
1
1
0
0
0
RPT2
1
1
0
0
0
0
0Fh
RPT1
1
0
0
0
0
0
Table 4: Alarm repeat
Once per second
Once per minute
Once per month
Alarm setting
Once per hour
Once per year
Once per day
Clock operation
HIGH-Z
10h
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