m41t81s STMicroelectronics, m41t81s Datasheet - Page 17

• Manufacturer Part Number: m41t81s
• Description: Serial Access Real-time Clock With Alarms
• Manufacturer: STMicroelectronics

Setting alarm clock registers
Note:
The IRQ/FT/OUT/SQW pin is an open drain output which requires a pull-up resistor to V
for proper operation. A 500-10k resistor is recommended in order to control the rise time.
The FT Bit is cleared on power-down.
Figure 11. Crystal accuracy across temperature
Figure 12. Clock calibration
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. It can also be programmed to go off while the
M41T81S is in the battery back-up mode to serve as a system wake-up call.
Bits RPT5-RPT1 put the alarm in the repeat mode of operation.
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/FT/OUT/SQW pin.
If the address pointer is allowed to increment to the Flags Register address, an alarm
condition will not cause the Interrupt/Flag to occur until the address pointer is moved to a
Frequency (ppm)
NORMAL
POSITIVE
CALIBRATION
NEGATIVE
CALIBRATION
–100
–120
–140
–160
–20
–40
–60
–80
20
0
–40
–30
–20
–10
0
10
Temperature °C
ΔF = K x (T – T
F
K
= –0.036 ppm/°C
20
T
30
O
= 25°C ± 5°C
O
)
2
40
2
± 0.006 ppm/°C
50
60
Table 3 on page 18
2
70
80
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