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STMicroelectronics M41T81SM6E
- Part No.:
- M41T81SM6E
- Manufacturer:
- STMicroelectronics
- Category:
- Real Time Clocks
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
M41T81SM6E.pdf
- Description:
- IC RTC CLK/CALENDAR I2C 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,512
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Product details
Overview
M41T81SM6E from STMicroelectronics is a serial real-time clock (RTC) IC with integrated 32.768 kHz crystal oscillator, I²C interface (400 kHz), ultra-low battery current (0.6 µA typ), and full calendar/date/time counters in BCD format - used for timekeeping and alarm functions in industrial control panels requiring long-term battery-backed operation.
For engineers reviewing the M41T81SM6E datasheet, M41T81SM6E pinout, M41T81SM6E application, or M41T81SM6E equivalent, key selection criteria include oscillator stability with embedded crystal, power-fail switchover behavior, programmable watchdog timer range (62.5 ms–128 s), software calibration capability, and battery-low flag signaling.
Technical Context
The M41T81SM6E implements a fully autonomous RTC core with automatic leap-year correction (valid until 2100), century-bit handling, and oscillator fail detection logic that monitors 32.768 kHz crystal operation in real time. Its internal power-sense circuit triggers seamless VCC-to-VBAT switchover at VSO (2.5 V ≤ VPFD ≤ 2.7 V) and maintains register integrity during brownout.
It operates as an I²C slave device (address 0xD0h) with auto-incrementing address pointer across 20 registers - including 8 clock/calendar bytes, 5 alarm bytes, 1 calibration byte, 1 watchdog byte, 1 flags byte, and 1 square-wave control byte - all accessible via standard START/STOP sequences with ACK/NACK protocol compliance.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Interface | I²C bus, 400 kHz max - enables direct connection to microcontroller I²C peripherals without level-shifting or timing margin concerns. |
| Battery Current | 0.6 µA typical - extends lithium coin-cell life beyond 10 years in backup mode, critical for unattended systems. |
| Operating Voltage | VCC = 2.0–5.5 V; VBAT ≥ 2.5 V - supports wide-input industrial power rails and ensures reliable switchover during 3.3 V or 5 V system brownouts. |
| Oscillator | Integrated 32.768 kHz crystal with 12.5 pF load capacitance - eliminates external capacitors and improves frequency stability over temperature (±20 ppm). |
| Watchdog Range | 62.5 ms to 128 s - provides precise timeout control for firmware recovery in embedded controllers without external timers. |
| Temperature Range | –40 °C to +85 °C - qualified for industrial environments including factory automation and outdoor metering enclosures. |
| Calendar Format | BCD-encoded century/year/month/date/day/hour/minute/second/tenths-hundredths - simplifies MCU parsing and avoids binary-to-BCD conversion overhead. |
Pinout & Package
Package: 8-pin SOIC (SO8), 150-mil body width, RoHS-compliant surface-mount package.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VCC | Main supply input | Accepts 2.0–5.5 V; powers RTC core and I²C interface during normal operation. |
| VSS | Ground reference | Common return path for all internal circuits and I²C pull-up resistors. |
| SCL | I²C clock input | Open-drain compatible; requires external pull-up; defines data sampling timing. |
| SDA | I²C bidirectional data | Open-drain; shares bus with other I²C slaves; supports multi-master arbitration. |
| IRQ/FT/OUT/SQW | Multi-function open-drain output | Configurable as alarm interrupt, frequency test signal, or square-wave output (1 Hz/32 Hz/1 kHz/4.096 kHz). |
| VBAT | Battery backup supply | Connects to lithium coin cell; powers RTC when VCC drops below switchover threshold (VSO). |
| XI | Crytal oscillator input | Internal connection to embedded 32.768 kHz crystal (SO8 variant); no external crystal required. |
| XO | Crytal oscillator output | Completes on-chip oscillator loop; tied internally to XI in SO8 package. |
Key Features
| Feature | Design Value |
|---|---|
| Embedded crystal oscillator | Eliminates external crystal and load capacitors, reducing BOM count and PCB footprint by 3 components. |
| Power-down time-stamp (HT bit) | Records hour-tens digit at power loss, enabling accurate elapsed-time calculation during battery-only operation. |
| Software clock calibration | Adjusts oscillator frequency via ±127 ppm fine-tuning register to compensate for crystal drift across temperature. |
| Alarm interrupt with battery-backup validity | Generates IRQ pulse even when VCC is absent - ensures time-triggered events execute reliably during mains failure. |
| Oscillator fail detection | Monitors crystal oscillation in real time and sets flag if stoppage occurs - prevents silent timekeeping failure in safety-critical systems. |
Applications
| Industrial PLC Time Stamping | Smart Energy Meter Logging |
|---|---|
Use Scenario: Recording timestamped sensor readings and event logs in programmable logic controllers deployed in factory automation lines. IC Role / Device Role / Timing Role: Primary RTC providing synchronized, battery-backed wall-clock time for data tagging and audit trail generation. Use Value: Ensures deterministic timestamp accuracy across power cycles and maintenance windows, meeting IEC 61131-3 logging requirements. | Use Scenario: Maintaining accurate billing intervals and outage records in residential/utility smart meters operating 15+ years on primary battery. IC Role / Device Role / Timing Role: Core timekeeping engine with automatic leap-year correction and century-bit support for long-duration deployment. Use Value: Delivers >10-year battery life with 0.6 µA backup current and eliminates manual date rollover errors through hardware-based calendar logic. |
| Medical Infusion Pump Scheduling | Building HVAC Controller Sync |
Use Scenario: Triggering drug delivery schedules and calibration reminders in battery-powered infusion pumps subject to FDA 21 CFR Part 11 audit trails. IC Role / Device Role / Timing Role: Certified time source for dose timing, alarm generation, and secure log entry timestamps. Use Value: Provides battery-backed alarm interrupts and oscillator fail detection - satisfying IEC 62304 safety requirement for time-critical therapeutic actions. | Use Scenario: Coordinating zone scheduling, occupancy sensing, and energy reporting across distributed HVAC controllers in commercial buildings. IC Role / Device Role / Timing Role: Network-synchronized RTC node enabling coordinated start/stop of chillers, fans, and dampers across multiple controllers. Use Value: Enables precise 1-second square-wave output for master-slave time alignment and reduces NTP dependency in isolated networks. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar real-time clock applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| DS3231M+ | Higher accuracy TCXO (±2 ppm), integrated temperature sensor, no embedded crystal in SO8 variant | Requires external crystal and compensation algorithm; better for precision metrology but higher BOM cost | Select when absolute time accuracy <±5 ppm is mandatory and board space allows crystal placement. |
| PCF8563T | Lower power (0.25 µA), no watchdog timer, no software calibration, no century bit support | Limited to basic timekeeping; lacks alarm repeat modes and power-down timestamp feature | Select only for cost-sensitive, low-feature applications where decade-long calendar support is not required. |
Compared with DS3231M+ and PCF8563T, the M41T81SM6E uniquely balances embedded crystal convenience, programmable watchdog, software calibration, and century-aware calendar - making it optimal for industrial systems needing robust, long-life timekeeping without external timing components.
Availability
M41T81SM6E is available at Aetrix Electronics and suitable for industrial PLCs, smart energy meters, medical infusion pumps, and building HVAC controllers requiring stable component supply across extended product lifecycles.
Supply support for M41T81SM6E 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 analog, MCU, power, and timing solutions for industrial, automotive, and consumer markets.
The M41T81SM6E belongs to ST's serial RTC product line, engineered specifically for battery-backed timekeeping in resource-constrained industrial systems where reliability, longevity, and minimal external components are critical design priorities.
FAQ
What is the function of the HT bit in the M41T81SM6E?
The HT (Hour-Tens) bit is part of the power-down time-stamp feature. When VCC fails and the device switches to VBAT, the current hour-tens digit is latched into this bit. This allows firmware to calculate exact elapsed time during battery-only operation by comparing pre- and post-failure hour values - essential for accurate uptime/downtime logging in industrial controllers.
Does the M41T81SM6E require external load capacitors for its crystal?
No. The M41T81SM6E integrates 12.5 pF load capacitance directly into the oscillator circuit. This eliminates the need for external capacitors when using the embedded crystal in the SO8 package, reducing component count, layout complexity, and potential tuning errors - a key differentiator versus discrete-crystal RTCs like the DS1307.
How does the oscillator fail detection work?
The oscillator fail detection circuit continuously monitors the 32.768 kHz signal amplitude and zero-crossing activity. If oscillation stops - due to crystal fracture, solder fatigue, or extreme temperature - the OFIE (Oscillator Fail Interrupt Enable) flag is set and the OF (Oscillator Fail) bit in the flags register becomes active. This condition persists until cleared by software, enabling immediate system-level fault response.
Can the M41T81SM6E generate multiple square-wave frequencies?
Yes. The SQW pin supports four selectable output frequencies: 1 Hz, 32 Hz, 1 kHz, and 4.096 kHz - configured via the square-wave control register (address 14h). This eliminates the need for external dividers or timers in applications requiring periodic wake-up signals, LED blinking, or clock synchronization pulses.
M41T81SM6E Specifications
- Product attributes
- Attribute value
- Manufacturer:
- STMicroelectronics
- Series:
- -
- Package/Case:
- 8-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tube
- Product Status:
- Obsolete
- 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:
- 2.7V ~ 5.5V
- Voltage - Supply, Battery:
- 2V ~ 3.5V
- Current - Timekeeping (Max):
- 100µA @ 2.7V ~ 5.5V
- Operating Temperature:
- -40°C ~ 85°C
- Mounting Type:
- Surface Mount
- Grade:
- -
- Qualification:
- -
- Supplier Device Package:
- 8-SOIC
M41T81SM6E FAQ
1.How can I place an order for M41T81SM6E through Aetrix?
Please submit a Request for Quotation (RFQ) for M41T81SM6E 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 M41T81SM6E reliable?
The price and inventory of M41T81SM6E are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for M41T81SM6E is usually 5 days.
3.What payment methods are accepted for M41T81SM6E?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for M41T81SM6E transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for M41T81SM6E?
M41T81SM6E orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your M41T81SM6E 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 M41T81SM6E?
For technical support, including M41T81SM6E datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your M41T81SM6E requirements.
6.How does Aetrix verify that M41T81SM6E is sourced from the original manufacturer or authorized distributors?
All M41T81SM6E 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 M41T81SM6E meets industry standards.
7.What is the process for return or replacement of M41T81SM6E?
All M41T81SM6E units undergo pre-shipment inspection (PSI). If there is an issue with M41T81SM6E, 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 M41T81SM6E part is unused and in its original packaging.
Return procedure for M41T81SM6E:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
M41T81SM6E Tags
-
MCP7940N-I/SN
Microchip Technology
-
MCP7940MT-I/MNY
Microchip Technology
-
PCF85063ATL/1,118
NXP USA Inc.
-
MCP7940NT-I/SN
Microchip Technology
-
MCP7940NT-I/MS
Microchip Technology
-
MCP7940N-I/MS
Microchip Technology
-
PCF85063AT/AY
NXP USA Inc.
-
PCF85063TP/1Z
NXP Semiconductors
-
PCF85063ATT/AJ
NXP USA Inc.
-
MCP7940NT-E/SN
Microchip Technology
-
MCP7940NT-I/MNY
Microchip Technology
-
MCP79400T-I/SN
Microchip Technology
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