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Serial real-time clock (RTC) with alarm
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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 (M41T62/63/64), programmable square wave output (M41T62/63/64), and watchdog output (M41T63/65). 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 mm x 3 mm 16-pin QFN which requires a user-supplied 32 KHz crystal, and an ultra-small 1.5 mm x 3.2 mm LCC with embedded crystal - no external crystal is required.

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Errata Sheet
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Key Features

  • Serial real-time clock (RTC) with alarm functions
  • 400 kHz I2C 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 I2C bus operating voltage
  • 4.4 V max VCCsuitable for lithium-ion battery operation
  • Low operating current of 35 μA (at 400 kHz)
  • 32 KHz square wave output is on at power-up. Suitable for driving a microcontroller in low-power mode. Can be disabled. (M41T62/63/64)
  • Programmable 1 Hz to 32 KHz square wave output (M41T62/63/64)
  • 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 mm x 3 mm, lead-free & halogen-free (ECOPACK2®) 16-lead QFN
  • Ultra-small 1.5 mm 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)

Circuit Diagram

Design Resources


Technical Documentation

Product Specifications

Description Version Size
DS3840: Low-power serial real-time clocks (RTCs) with alarm
20.0 1,755 KB

Application Notes

Description Version Size
AN1011: Battery technology used in NVRAM and real-time clock (RTC) products from ST
4.0 248 KB
AN1216: Implementing a periodic alarm with TIMEKEEPER® and serial real-time clocks (RTCs)
2.0 193 KB
AN1336: Power-fail comparator for NVRAM supervisory devices
2.0 128 KB
AN1572: Power-down time-stamp function in serial real-time clocks (RTCs)
2.0 171 KB
AN3060: Applications guide for serial real-time clocks (RTCs)
2.1 370 KB
AN923: Managing century information using serial real-time clocks and TIMEKEEPER® NVRAMs
3.0 195 KB
AN934: How to use the digital calibration feature in TIMEKEEPER® and serial real-time clock (RTC) products
4.1 123 KB

Related Tools and Software

Related Tools and Software

Part Number Description
STEVAL-SCM001V1 RTC dongle demonstration board based on the M41T62 and ST72651AR6
STSW-SRTC001 I2C code for Serial RTC
STSW-SRTC002 SPI code -Serial RTC

Publications and Collaterals


Description Version Size
Serial real-time clock ICs
827 KB

Sample & Buy

Part Number Marketing StatusPackagePacking TypeOperating Temperature (min) Operating Temperature (max) NVRAM sizeAutomotive GradeOrder From STUnit Price (US$)*
@ 1000
Distributor AvailabilityRoHS Compliance GradeDownload
Material Declaration**
M41T62LC6FActiveLCC8 3.2x1.5 mmTape And Reel-4085_-2.3Distributor reported inventory date: 2014-10-20
Distributor NameRegionStockMin. order
ARROWOrder NowAMERICA59451000
M41T62Q6FActiveVFQFPN 16 3x3x0.9Tape And Reel-4085_-.9Distributor reported inventory date: 2014-10-20
Distributor NameRegionStockMin. order
ARROWOrder NowAMERICA11293000
Newark Element14Order NowAMERICA2140
Farnell Element14Order NowEUROPE54211

(*) Suggested Resale Price per unit (USD) for BUDGETARY USE ONLY. For quotes, prices in local currency, please contact your local ST Sales Office or our Distributors
(**) The Material Declaration forms available on may be generic documents based on the most commonly used package within a package family. For this reason, they may not be 100% accurate for a specific device. Please contact our sales support for information on specific devices.
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