Datasheet

M41T81S Clock operation
Doc ID 10773 Rev 7 17/32
The IRQ/FT/OUT/SQW pin is an open drain output which requires a pull-up resistor to V
CC
for proper operation. A 500-10 k 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
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. It can also be programmed to go off while the
M41T81S is in the battery backup mode to serve as a system wake-up call.
Bits RPT5-RPT1 put the alarm in the repeat mode of operation. Table 3 on page 19 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.
AI07888
–160
0 10203040506070
Frequency (ppm)
Temperature °C
80–10–20–30–40
–100
–120
–140
–40
–60
–80
20
0
–20
= –0.036 ppm/°C
2
± 0.006 ppm/°C
2
K
ΔF
= K x (T – T
O
)
2
F
T
O
= 25°C ± 5°C
AI00594B
NORMAL
POSITIVE
CALIBRATION
NEGATIVE
CALIBRATION