M41T81:Serial real-time clock (RTC) with alarm

The M41T81 is a low-power serial 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 M41T81 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 SRAM and 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 M41T81 is supplied in an 8-pin SOIC.

Key Features

  • For all new designs use M41T81S
  • Counters for tenths/hundredths of seconds, seconds, minutes, hours, day, date, month, year, and century
  • 32 KHz crystal oscillator integrating load capacitance (12.5 pF) providing exceptional oscillator stability and high crystal series resistance operation
  • Serial interface supports I2 C bus (400 kHz protocol)
  • Ultra-low battery supply current of 0.6 μA (typ at 3 V)
  • 2.0 to 5.5 V clock operating voltage
  • Automatic switchover and deselect circuitry (for 3 V application select M41T81S datasheet)
  • Power-down time stamp (HT bit) allowing determination of time elapsed in battery backup
  • 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 crystal deviation due to temperature
  • Operating temperature of –40 to 85 °C
  • ECOPACK® package available
Product Specifications
DescriptionVersionSize
DS2149: Serial access real-time clock with alarm11.0583 KB
Application Notes
DescriptionVersionSize
AN3060: Applications guide for serial real-time clocks (RTCs)3.0878 KB
AN1011: Battery technology used in NVRAM and real-time clock (RTC) products from ST4.0248 KB
AN934: How to use the digital calibration feature in TIMEKEEPER® and serial real-time clock (RTC) products4.1123 KB
AN1216: Implementing a periodic alarm with TIMEKEEPER® and serial real-time clocks (RTCs)2.0192 KB
AN4641: Integrating TIMEKEEPER® and real-time clock supervisor functions1.0479 KB
AN923: Managing century information using serial real-time clocks and TIMEKEEPER® NVRAMs4.0142 KB
AN1572: Power-down time-stamp function in serial real-time clocks (RTCs)2.0171 KB
AN1336: Power-fail comparator for NVRAM supervisory devices2.0127 KB
AN1012: Predicting the battery life and data retention period of NVRAMs and serial RTCs4.1439 KB
AN922: Using a Super Cap to back up the M41T56, M41T00, M41T11, M41T81, M41T94, and M41ST84W (16-pin)2.184 KB
HW Model & CAD Libraries
DescriptionVersionSize
Ibis model1.08 KB
Brochures
DescriptionVersionSize
Serial real-time clock ICs1.0827 KB
Clocks and Timers Software
Part NumberManufacturerDescription
STSW-SRTC001STI2C code for Serial RTC
STSW-SRTC002STSPI code -Serial RTC
Sample & Buy
Part NumberPackagePacking TypeOperating Temperature (°C) (min)Operating Temperature (°C) (max)Unit Price (US$) *QuantityNVRAM size (B)ECCN (EU)ECCN (US)Country of Origin
M41T81M6FSO-8Tape And Reel-40851.1061000-NECEAR99-
Quality & Reliability
Part NumberPackageGradeRoHS Compliance GradeMaterial Declaration**
M41T81M6FSO-8IndustrialEcopack1md_o7-wspc-so-wspc-08-wspc-.15-wspc-jedec_bazma6aac81-wspc-(m41t81sm6f).pdf
md_o7-wspc-so-wspc-08-wspc-.xml
Serial access real-time clock with alarm M41T81
circuit_diagram_7529_thumbnail.png M41T81
串行实时时钟(RTC)应用指南 M41T60
ST NVRAM 和实时时钟(RTC)产品中使用的电池技术 M4Z28-BR00SH
How to use the digital calibration feature in TIMEKEEPER® and serial real-time clock (RTC) products M41T60
Implementing a periodic alarm with TIMEKEEPER® and serial real-time clocks (RTCs) M41T94
集成TIMEKEEPER® 与实时时钟监控器功能 M41T60
Managing century information using serial real-time clocks and TIMEKEEPER® NVRAMs M41T60
串行实时时钟(RTC)的掉电时间戳功能 M41T60
Power-fail comparator for NVRAM supervisory devices M41T60
预测NVRAM 和串行RTC 的电池寿命和数据保存期限 M4Z28-BR00SH
使用Super Cap 为M41T56、M41T00、M41T11、M41T81、M41T94 和M41ST84W (16 引脚)提供备用电源 M41T94
Using a Super Cap to back up the M41T56, M41T00, M41T11, M41T81, M41T94, and M41ST84W (16-pin) M41T81
Predicting the battery life and data retention period of NVRAMs and serial RTCs M4T28-BR12SH
md_o7-wspc-so-wspc-08-wspc-.15-wspc-jedec_bazma6aac81-wspc-(m41t81sm6f).pdf M41T81
md_o7-wspc-so-wspc-08-wspc-.xml TS4871