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Home > Products > Integrated Circuits (ICs) > Clock/Timing > Real Time Clocks

STMicroelectronics M41T81M6F

Name: M41T81M6F
Brand: STMicroelectronics
SKU: M41T81M6F
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: M41T81M6F

Manufacturer:: STMicroelectronics

Category:: Real Time Clocks

Package:: 8-SOIC (0.154", 3.90mm Width)

Datasheet:: M41T81M6F.pdf

Description:: IC RTC CLK/CALENDAR I2C 8SOIC

Quantity:: RFQ Add To RFQ list

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Inventory:10,812

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Product details

Overview

M41T81M6F from STMicroelectronics is a serial real-time clock (RTC) with integrated 32.768 kHz crystal oscillator, alarm, watchdog timer, and programmable square wave output. It maintains time-of-day/calendar in BCD format across power loss using battery backup, supports I²C interface at 400 kHz, operates from 2.0–5.5 V, and delivers ultra-low 0.6 µA battery current at 3 V.

For engineers reviewing the M41T81M6F datasheet, M41T81M6F pinout, M41T81M6F application, or M41T81M6F equivalent, this device serves as a precision timekeeping solution for embedded systems requiring automatic leap-year correction, power-fail timestamping, and battery-backed alarm/wake-up functionality.

Technical Context

The M41T81M6F implements a fully autonomous RTC core with hardware-based calendar logic that automatically adjusts for 28–31 day months and leap years through year 2100. Its on-die oscillator integrates 12.5 pF load capacitance, enabling stable operation with high-series-resistance crystals.

It features dual-power architecture with seamless switchover between V_CC and V_BAT, HT-bit timestamping of power-down events, and a software-calibratable clock to compensate for temperature-induced crystal drift. The I²C interface uses standard 7-bit slave address 0xD0h and supports sequential read/write across 20 registers.

Key Specifications

Parameter	Value and Actual Design Meaning
Interface	I²C bus, 400 kHz protocol - enables direct connection to microcontrollers without level-shifting or additional timing logic.
Operating Voltage	2.0–5.5 V - supports wide-range supply rails including 3.3 V and 5 V systems without external regulators.
Battery Current	0.6 µA (typ at 3 V) - extends lithium button cell life beyond 10 years in backup mode.
Temperature Range	–40 °C to +85 °C - qualified for industrial and automotive cabin environments.
Timekeeping Accuracy	Crystal-dependent; calibrated via software register - allows ±5 ppm compensation over temperature without external components.
Alarm Function	Programmable down to second granularity, active during battery backup - enables wake-up from deep sleep without host intervention.
Watchdog Timer	62.5 ms to 128 s range, independent of main clock - provides fail-safe system recovery even if RTC registers are corrupted.

Pinout & Package

Supplied in an 8-pin SOIC (SO8) package with 150-mil body width, compliant with ECOPACK® environmental standards.

Pin/Terminal	Circuit Role	Design Meaning
V_CC	Main supply voltage input	Primary power source; device switches to V_BAT when V_CC drops below V_SO (V_BAT – 0.5 V typ).
V_SS	Ground reference	Common return path for all internal circuitry and I²C pull-ups.
SCL	I²C clock input	Master-generated synchronous clock; requires external pull-up resistor.
SDA	I²C bidirectional data line	Open-drain interface; requires external pull-up resistor and supports multi-master arbitration.
IRQ/FT/OUT/SQW	Multi-function open-drain output	Configurable as alarm interrupt, frequency test signal, general-purpose output, or square wave (highest priority: SQW).
V_BAT	Battery backup supply	Provides continuous power to RTC and SRAM during main supply failure; no external diode required.
XI	Cry stal oscillator input	Connects to one terminal of external 32.768 kHz tuning fork crystal.
XO	Cry stal oscillator output	Connects to other terminal of external crystal; internal 12.5 pF load capacitance eliminates need for external caps.

Key Features

Feature	Design Value
Automatic calendar correction	Hardware handles 28–31 day months and leap years through year 2100 - eliminates firmware date math and reduces MCU overhead.
Power-down time stamp (HT bit)	Hardware sets HT=1 on V_CC drop - enables precise determination of power-loss instant without external supervision.
Software clock calibration	Adjusts oscillator frequency via 7-bit trim register - compensates crystal aging and thermal drift without hardware modification.
Programmable square wave output	Configurable frequencies: 32.768 kHz, 1.024 kHz, 32 Hz, or 1 Hz - replaces external clock dividers for system timing or LED blinking.
Ultra-low backup current	0.6 µA typical at 3 V - permits use of CR1220 or BR1225 coin cells for >10-year battery life in standby.

Applications

Industrial PLCs

Smart Energy Meters

Use Scenario: Maintaining accurate billing timestamps and firmware update logs during grid outages.

IC Role / Device Role / Timing Role: Primary timekeeping and alarm-triggered event logging under battery backup.

Use Value: Guarantees traceable, tamper-resistant time stamps for regulatory compliance and audit trails.

Use Scenario: Recording energy consumption intervals and detecting power anomalies across seasonal load cycles.

IC Role / Device Role / Timing Role: High-accuracy calendar and interval timer synchronized to utility grid cycles.

Use Value: Enables precise 15-min or hourly metering windows with automatic month-end rollover and leap-year handling.

Medical Diagnostic Devices

Network Routers & Switches

Use Scenario: Timestamping patient vital sign captures and diagnostic report generation in portable ultrasound units.

IC Role / Device Role / Timing Role: Battery-backed real-time clock with alarm-driven data capture triggers.

Use Value: Ensures HIPAA-compliant audit logs remain synchronized across device reboots and battery swaps.

Use Scenario: Synchronizing SNMP trap timestamps and firmware upgrade scheduling across distributed infrastructure.

IC Role / Device Role / Timing Role: System-level time anchor for NTP client fallback and secure boot validation windows.

Use Value: Prevents certificate expiration errors and log correlation failures during WAN outages.

Equivalent & Alternatives

The following parts are listed as comparable options for similar real-time clock applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
DS3231SN#T&R	Integrated TCXO (±2 ppm accuracy), higher cost, no software calibration needed.	Preferred where absolute accuracy <±3 ppm is required without firmware tuning.	Select DS3231 when guaranteed long-term stability outweighs cost and design flexibility.
M41T81S	Pin-compatible successor with enhanced power switchover logic and updated qualification for new designs.	Recommended for all new designs per ST's official guidance; identical register map and footprint.	Choose M41T81S for production ramp to ensure lifecycle support and latest reliability data.

Compared with DS3231SN#T&R, M41T81M6F trades absolute accuracy for lower cost and software-adjustable calibration; compared with M41T81S, it lacks updated power-fail hysteresis but remains functionally identical in legacy systems.

Availability

M41T81M6F is available at Aetrix Electronics and suitable for industrial PLCs, smart energy meters, medical diagnostic devices, and network routers requiring stable component supply with long-term availability and full traceability.

Supply support for M41T81M6F includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

STMicroelectronics is a global semiconductor leader headquartered in Geneva, specializing in microcontrollers, power management, sensors, and timing solutions for industrial, automotive, and consumer markets.

The M41T81M6F belongs to ST's serial RTC product line, designed specifically for cost-sensitive, battery-backed embedded systems needing robust calendar functionality, alarm/wake-up capability, and seamless power-fail resilience.

FAQ

What is the function of the HT bit in the M41T81M6F?

The HT (Halt Time) bit is automatically set to '1' when V_CC falls below the switchover threshold, freezing the TIMEKEEPER® registers to preserve the exact time of power loss. Reading the clock registers while HT=1 returns the last valid time before failure. Clearing HT to '0' resumes normal timekeeping and updates.

Can the M41T81M6F operate without an external crystal?

No - the M41T81M6F requires an external 32.768 kHz tuning-fork crystal connected between XI and XO pins. Its internal oscillator circuit includes integrated 12.5 pF load capacitance, eliminating the need for external capacitors, but the crystal itself is mandatory for timekeeping.

How does the alarm function behave during battery backup mode?

The alarm remains fully operational during battery backup: it can generate IRQ pulses or toggle the SQW output even when V_CC is absent. This enables reliable wake-up from deep-sleep states without host processor involvement, critical for low-power sensor nodes and metering applications.

Is the M41T81M6F pin-compatible with the M41T81S?

Yes - M41T81M6F and M41T81S share identical 8-pin SOIC packaging, pinout, register map, and I²C addressing. The M41T81S improves power switchover behavior and qualifies for new designs per ST's documentation, but M41T81M6F remains functionally interchangeable in existing layouts.

M41T81M6F Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: 8-SOIC (0.154", 3.90mm Width)

Packaging:: Tape & Reel (TR)

Product Status:: Active

Programmable:: Not Verified

Type:: Clock/Calendar

Features:: Alarm, Leap Year, Square Wave Output, Watchdog Timer

Memory Size:: -

Time Format:: HH:MM:SS:hh (24 hr)

Date Format:: YY-MM-DD-dd

Interface:: I2C, 2-Wire Serial

Voltage - Supply:: 2V ~ 5.5V

Voltage - Supply, Battery:: 2.5V ~ 3.5V

Current - Timekeeping (Max):: 100µA @ 2V ~ 5.5V

Operating Temperature:: -40°C ~ 85°C

Mounting Type:: Surface Mount

Grade:: -

Qualification:: -

Supplier Device Package:: 8-SOIC

M41T81M6F FAQ

1.How can I place an order for M41T81M6F through Aetrix?

Please submit a Request for Quotation (RFQ) for M41T81M6F on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for M41T81M6F reliable?

The price and inventory of M41T81M6F are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for M41T81M6F is usually 5 days.

3.What payment methods are accepted for M41T81M6F?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for M41T81M6F transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for M41T81M6F?

M41T81M6F orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your M41T81M6F order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for M41T81M6F?

For technical support, including M41T81M6F datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your M41T81M6F requirements.

6.How does Aetrix verify that M41T81M6F is sourced from the original manufacturer or authorized distributors?

All M41T81M6F products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that M41T81M6F meets industry standards.

7.What is the process for return or replacement of M41T81M6F?

All M41T81M6F units undergo pre-shipment inspection (PSI). If there is an issue with M41T81M6F, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The M41T81M6F part is unused and in its original packaging.

Return procedure for M41T81M6F:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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