M41T81S datasheet(17/31 Pages) STMICROELECTRONICS

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M41T81S

Clock operation

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The IRQ/FT/OUT/SQW pin is an open drain output which requires a pull-up resistor to VCC

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

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 back-up 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 18 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/FT/OUT/SQW pin.

Note:

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

AI07888

–160

10203040506070

Frequency (ppm)

Temperature

°C

–10

–20

–30

–40

–100

–120

–140

–40

–60

–80

–20

= –0.036 ppm/

°C

2 ± 0.006 ppm/°C2

ΔF

= K x (T – T

O = 25°C ± 5°C

AI00594B

NORMAL

POSITIVE

CALIBRATION

NEGATIVE

CALIBRATION

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