STMicroelectronics M41T81MX6

Overview

M41T81MX6 from STMicroelectronics is a serial-access 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 via automatic VCC-to-VBAT switchover, supports I²C at 400 kHz, operates from 2.0–5.5 V, and delivers 0.6 µA typical battery current at 3 V.

For engineers reviewing the M41T81MX6 datasheet, M41T81MX6 pinout, M41T81MX6 application, or M41T81MX6 equivalent, this page provides verified technical context, validated pin functions, confirmed alarm/wdog calibration behavior, and production-ready supply guidance for industrial timing systems requiring century-aware calendar accuracy and battery-backed timestamping.

Technical Context

The M41T81MX6 implements a fully autonomous RTC core with hardware-based leap-year correction (valid through year 2100), automatic month-length adjustment (28–31 days), and century-bit toggle control (CEB/CB). Its internal BiPORT™ register architecture separates user-accessible clock registers (00h–07h) from control/alarm/wdog registers (08h–13h), preventing read-modify-write corruption during time updates.

It features dual-power sensing: VSO = VBAT – 0.5 V (typ) triggers seamless switchover to battery backup, while HT bit latching preserves exact power-down timestamp. The IRQ/FT/OUT/SQW pin supports four prioritized functions-interrupt, frequency test, open-drain output, and square wave-with square wave having highest priority.

Key Specifications

Pinout & Package

Package: 8-pin SOIC (SO8), 150-mil body width, ECOPACK® RoHS-compliant surface-mount package.

Key Features

Applications

Equivalent & Alternatives

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

Compared with M41T81MX6, M41T81S offers backward-compatible enhancements for long-term design sustainability, while DS3231M trades calendar robustness and power-loss forensics for superior oscillator accuracy-making M41T81MX6 optimal for cost-sensitive, century-aware industrial timing where battery longevity and failure diagnostics are critical.

Availability

M41T81MX6 is available at Aetrix Electronics and suitable for smart metering, industrial PLCs, medical infusion pumps, and building HVAC controllers requiring stable component supply, long-term lifecycle assurance, and RoHS-compliant packaging.

Supply support for M41T81MX6 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, Switzerland, designing and manufacturing microcontrollers, power ICs, sensors, and timing solutions for industrial, automotive, and consumer markets.

The M41T81MX6 belongs to ST's legacy RTC product line, engineered specifically for battery-backed, calendar-aware timekeeping in resource-constrained embedded systems where reliability, low power, and long-term availability are paramount.

FAQ

What is the function of the HT bit in the M41T81MX6?

The HT (Halt Time) bit is a hardware-latched flag that automatically sets to '1' at the instant VCC falls below VSO, freezing the TIMEKEEPER® registers. This allows the host system to read the exact time of power failure upon restoration. Clearing HT to '0' resumes normal timekeeping; the bit is not self-clearing and requires explicit write access to register 03h bit D4.

Does the M41T81MX6 support leap-year correction beyond year 2099?

Yes-the M41T81MX6 implements leap-year logic valid through year 2100 using the CE (Century Enable) and CB (Century Bit) in register 03h. When CE=1, CB toggles at century boundaries, enabling correct February 29 handling in years 2000 and 2100. This satisfies Y2100 compliance for industrial calendar applications.

Can the IRQ/FT/OUT/SQW pin generate simultaneous square wave and alarm interrupt signals?

No-the IRQ/FT/OUT/SQW pin supports only one active function at a time, with fixed hardware priority: square wave > frequency test > output driver > alarm interrupt. If square wave is enabled, alarm interrupts are suppressed on that pin; separate polling of alarm status register (09h bit D0) is required to detect pending alarms.

Is external load capacitance required for the 32.768 kHz crystal?

No-the M41T81MX6 integrates 12.5 pF load capacitance internally, eliminating the need for external capacitors. This simplifies PCB layout, reduces BOM count, and improves oscillator stability across temperature and aging, especially with high-series-resistance crystals common in industrial environments.