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Serial real-time clock (RTC) with alarm

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1 - 9$6.330%
10 - 20$5.7210%
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Parameter NameParameter Value
Operating RangeIndustrial
Supply Voltage Min Volt2.7
Supply Voltage Max Volt5.5
Operating Temp Min Celsius-40.0
Operating Temp Max Celsius85.0
Packing TypeTape And Reel
RoHs compliantEcopack1
Package NameSO18 with embedded crystal

The M41T81S is a low-power serial real-time clock (RTC) with a built-in 32.768 kHz oscillator (external crystal controlled). Eight bytes of the SRAM are used for the clock/calendar function and are configured in binary-coded decimal (BCD) format. An additional 12 bytes of SRAM provide status/control of alarm, watchdog and square wave functions. Addresses and data are transferred serially via a two line, bidirectional I2C interface. The built-in address register is incremented automatically after each WRITE or READ data byte.

The M41T81S has a built-in power sense circuit which detects power failures and automatically switches to the battery supply when a power failure occurs. The energy needed to sustain the clock operations can be supplied by a small lithium button supply when a power failure occurs. Functions available to the user include a non-volatile, time-of-day clock/calendar, alarm interrupts, watchdog timer and programmable square wave output. The eight clock address locations contain the century, year, month, date, day, hour, minute, second and tenths/hundredths of a second in 24-hour BCD format. Corrections for 28, 29 (leap year - valid until year 2100), 30 and 31 day months are made automatically.

The M41T81S is supplied in either an 8-pin SOIC or an 18-pin 300 mil SOIC package which includes an embedded 32 KHz crystal.

The 18-pin, embedded crystal SOIC requires only a user-supplied battery to provide non-volatile operation.

Key features
  • Counters for tenths/hundredths of seconds, seconds, minutes, hours, day, date, month, year, and century
  • 32 KHz crystal oscillator with integrated load capacitance (12.5 pf) which provides exceptional oscillator stability and high crystal series resistance operation)
  • Oscillator stop detection (monitors clock operation)
  • Serial interface supports I2C bus (400 kHz protocol)
  • Ultra-low battery supply current of 0.6 μA (typ)
  • 2.0 to 5.5 V clock operating voltage
  • Automatic switchover and deselect circuitry (fixed reference) which provides full operation in 3.0 V applications)
  • VCC= 2.7 to 5.5 V
  • 2.5 V ≤ VPFD≤ 2.7 V
  • Power-down time-stamp (HT bit) which allows determination of time elapsed in battery backup
  • Battery low flag
  • Programmable alarm and interrupt function (valid even during battery backup mode)
  • Accurate programmable watchdog timer (from 62.5 ms to 128 s)
  • Software clock calibration (to compensate for crystal deviation due to temperature)
  • Operating temperature of –40 to 85 °C
  • Package options include an 8-lead SOIC or 18-lead embedded crystal SOIC