STMicroelectronics M41T81M6E

Overview

M41T81M6E 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 provides BCD-formatted timekeeping (century, year, month, date, day, hour, minute, second, tenths/hundredths), automatic leap-year correction through 2100, ultra-low 0.6 µA battery current at 3 V, and I²C interface compliance at 400 kHz - deployed in industrial control panels for timestamped event logging during mains failure.

For engineers reviewing the M41T81M6E datasheet, M41T81M6E pinout, M41T81M6E application, or M41T81M6E equivalent, this page delivers verified specifications, validated SOIC-8 pin functions, confirmed alarm/watchdog timing behavior, and direct substitution guidance for legacy RTC replacement in battery-backed embedded systems.

Technical Context

The M41T81M6E implements a fully autonomous RTC core with internal BiPORT™ register architecture: external clock registers (00h–07h) are updated only after internal divider chain completion, preventing mid-read corruption. Its oscillator integrates 12.5 pF load capacitance and supports high-series-resistance crystals for stable operation across –40 to +85 °C.

Power management includes automatic VCC-to-VBAT switchover at VSO = VBAT – 0.5 V (typ), HT-bit timestamping of power-down events, and write-protection recovery window (trec) on VCC restoration. Alarm and watchdog functions remain active in battery backup mode, with interrupt asserted on IRQ/FT/OUT/SQW open-drain pin.

Key Specifications

Pinout & Package

Supplied in an 8-pin SOIC (SO8) package per JEDEC MS-012, 150-mil body width, with standard gull-wing lead form for reflow-compatible PCB assembly.

Key Features

Applications

Equivalent & Alternatives

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

Compared with M41T81M6E, M41T81S delivers tighter power-switching control for 3 V rails, while DS1307 omits critical features like oscillator integration and power-failure forensics - making M41T81M6E the optimal balance of feature completeness, accuracy, and industrial robustness.

Availability

M41T81M6E is available at Aetrix Electronics and suitable for industrial data loggers, smart energy meters, building automation controllers, and medical diagnostic devices requiring stable component supply across multi-year production cycles.

Supply support for M41T81M6E 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, delivering silicon solutions for automotive, industrial, and power management applications.

The M41T81 belongs to ST's precision timing product line, engineered specifically for battery-backed, high-reliability RTC applications in industrial and metering systems where accuracy, longevity, and power resilience are mandatory.

FAQ

What is the function of the HT bit in the M41T81M6E?

The HT (Halt Time) bit is a hardware-latched flag that automatically sets to '1' upon VCC failure, freezing the TIMEKEEPER® registers at the exact moment of power loss. This enables firmware to read the precise time of brownout or blackout events. Clearing HT to '0' resumes normal timekeeping. The bit is retained in battery backup mode and requires no external supervision.

Does the M41T81M6E require external load capacitors for the 32.768 kHz crystal?

No. The M41T81M6E integrates 12.5 pF load capacitance directly into its XI/XO oscillator circuitry, eliminating the need for external capacitors. This simplifies PCB layout, improves oscillator start-up reliability across temperature, and reduces bill-of-materials cost - confirmed in Section 3.2 and Table 10 of the official datasheet.

Can the alarm function operate while the device is in battery backup mode?

Yes. The alarm circuit remains fully functional during battery backup operation. When configured, it asserts an interrupt on the IRQ/FT/OUT/SQW pin regardless of VCC status. This allows host systems to wake from deep sleep or trigger latching circuits even during extended mains outages - a key capability documented in Sections 3.4 and 4.1 of the datasheet.

What is the maximum I²C clock frequency supported by the M41T81M6E?

The M41T81M6E supports standard-mode and fast-mode I²C operation up to 400 kHz, as specified in Section 2.1 and Table 13 of the datasheet. It does not support high-speed mode (3.4 MHz). Timing parameters including tSU:DAT, tHD:STA, and tLOW are fully characterized for 400 kHz operation under all voltage and temperature conditions.