5.0 V, 3.3/3.0 V secure real-time clock , NVRAM supervisor with tamper detection and 128 bytes of clearable NVRAM

The M41ST87Y/W secure serial RTC and NVRAM supervisor is a low power 1280-bit, static CMOS SRAM organized as 160 bytes by 8 bits. A built-in 32.768 kHz oscillator (internal crystal-controlled) and 8 bytes of the SRAM are used for the clock/calendar function and are configured in binary coded decimal (BCD) format.

An additional 11 bytes of RAM provide calibration, status/control of alarm, watchdog, tamper, and square wave functions. 8 bytes of ROM and finally 128 bytes of user RAM are also provided. 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 M41ST87Y/W 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-cell supply when a power failure occurs.

Functions available to the user include a non-volatile, time-of-day clock/calendar, alarm interrupts, tamper detection, watchdog timer, and programmable square wave output. Other features include a power-on reset as well as two additional debounced inputs (RSTIN1and RSTIN2) which can also generate an output reset (RST). 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.

Key Features

  • 5.0, 3.3, or 3.0 V operation
  • 400 kHz I2 C bus
  • NVRAM supervisor to non-volatize external LPSRAM
  • 2.5 to 5.5 V oscillator operating voltage
  • Automatic switchover and deselect circuitry
  • Choice of power-fail deselect voltages
    • M41ST87Y: (not recommended for new design, contact ST sales office for availability) THS = 1: VPFD ≈ 4.63 V; VCC = 4.75 to 5.5 V THS = 0: VPFD ≈ 4.37 V; VCC = 4.5 to 5.5 V
    • M41ST87W: THS = 1: VPFD ≈ 2.9 V; VCC = 3.0 to 3.6 V THS = 0: VPFD ≈ 2.63 V; VCC = 2.7 to 3.6 V
  • Two independent power-fail comparators (1.25 V reference)
  • Counters for tenths/hundredths of seconds, seconds, minutes, hours, day, date, month, year, and century
  • 128 bytes of clearable, general purpose NVRAM
  • Programmable alarm and interrupt function (valid even during battery backup mode)
  • Programmable watchdog timer
  • Unique electronic serial number (8-byte)
  • 32 kHz frequency output available upon power-on
  • Microprocessor power-on reset output
  • Battery low flag
  • Ultra-low battery supply current of 500 nA (typ)
  • Security features
    • Tamper indication circuits with timestamp and RAM clear
    • LPSRAM clear function (TPCLR )
    • Packaging includes a 28-lead, embedded crystal SOIC and a 20-lead SSOP
    • Oscillator stop detection


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Description Version Size
DS3301 DS3301: 5.0 V and 3.3/3.0 V secure serial RTC and NVRAM supervisor with tamper detection and 128 bytes of clearable NVRAM 11.0 1 MB
Description Version Size
AN3060 AN3060: 串行实时时钟(RTC)应用指南 3.0 453 KB
AN1011 AN1011: ST NVRAM 和实时时钟(RTC)产品中使用的电池技术 4.0 416 KB
AN1879 AN1879: 如何使用M41ST87W的入侵检测及RAM清除功能 5.0 455 KB
AN934 AN934: How to use the digital calibration feature in TIMEKEEPER® and serial real-time clock (RTC) products 4.1 123 KB
AN1216 AN1216: Implementing a periodic alarm with TIMEKEEPER® and serial real-time clocks (RTCs) 2.0 192 KB
AN4641 AN4641: 集成TIMEKEEPER® 与实时时钟监控器功能 1.0 508 KB
AN923 AN923: Managing century information using serial real-time clocks and TIMEKEEPER® NVRAMs 4.0 142 KB
AN1572 AN1572: 串行实时时钟(RTC)的掉电时间戳功能 2.0 394 KB
AN1336 AN1336: Power-fail comparator for NVRAM supervisory devices 2.0 127 KB
AN1012 AN1012: 预测NVRAM 和串行RTC 的电池寿命和数据保存期限 4.1 813 KB

HW Model & CAD Libraries

HW Model & CAD Libraries
Description Version Size
Ibis model 1.0 14 KB


Description Version Size
Serial real-time clock ICs 1.0 827 KB


Clocks and Timers Software


型号 Package Packing Type Operating Temperature (°C) (min) Operating Temperature (°C) (max) Marketing Status Unit Price (US$) * Quantity NVRAM size (B) ECCN (EU) ECCN (US) Country of Origin More info Order from ST Order from Distributors
M41ST87WSS6F SSOP 20 7.2x5.3 Tape And Reel -40 85 Active - - 128 NEC EAR99 MALAYSIA MORE INFO 获取样片 Add to cart DISTRIBUTOR AVAILABILITY

(*) 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


型号 Marketing Status Package Grade RoHS Compliance Grade Material Declaration**
M41ST87WMX6TR ActiveSO28 WITH EMBEDDED CRYSTALIndustrialEcopack1 0 0
M41ST87WSS6F ActiveSSOP 20 7.2x5.3IndustrialEcopack2 0 0

(**) The Material Declaration forms available on st.com 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.