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M41T65：Low-power serial real-time clock (RTC) with alarm

The M41T6x is a low-power serial real-time clock (RTC) with a built-in 32.768 kHz oscillator. Eight registers are used for the clock/calendar function and are configured in binary-coded decimal (BCD) format. An additional eight registers provide status/control of alarm, 32 KHz output, calibration, and watchdog 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.

Functions available to the user include a time-of-day clock/calendar, alarm interrupts (M41T62/65), 32 KHz output (M41T62/64), programmable square wave output (M41T62/64), and watchdog output (M41T65). 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), 30- and 31-day months are made automatically.

The M41T6x is supplied in two very small packages: a tiny, 3 x 3 mm 16-pin QFN which requires a user-supplied 32 KHz crystal, and an ultra-small 1.5 x 3.2 mm LCC with embedded crystal - no external crystal is required.

Key Features

• Serial real-time clock (RTC) with alarm functions
  • 400 kHz I2 C serial interface
  • Memory mapped registers for seconds, minutes, hours, day, date, month, year, and century
  • Tenths/hundredths of seconds register
• 350 nA timekeeping current at 3 V
• Timekeeping down to 1.0 V
• 1.3 V to 4.4 V I2 C bus operating voltage
  • 4.4 V max VCC suitable for lithium-ion battery operation
• Low operating current of 35 μA (at 400 kHz I2 C speed)
• 32 KHz square wave output is on at power-up. Suitable for driving a microcontroller in low-power mode. Can be disabled. (M41T62/64)
• Programmable 1 Hz to 32 KHz square wave output (M41T62/64)
• Programmable alarm with interrupt function (M41T62/65)
• 32 KHz crystal oscillator integrates crystal load capacitors, works with high series resistance crystals
• Oscillator stop detection monitors clock operation
• Accurate programmable watchdog
  • 62.5 ms to 31 min timeout
• Software clock calibration. Can adjust timekeeping to within ±2 parts per million (±5 seconds per month)
• Automatic leap year compensation
• –40 to +85 °C operation
• Two package options:
  • Very small 3 x 3 mm, lead-free & halogen-free (ECOPACK2® ) 16-lead QFN
  • Ultra-small 1.5 x 3.2 mm, lead-free & halogen-free (ECOPACK2® ) 8-pin ceramic leadless chip carrier with embedded 32 KHz crystal - no external oscillator components required (M41T62)

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