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

STMicroelectronics M41T256YMH7E

Name: M41T256YMH7E
Brand: STMicroelectronics
SKU: M41T256YMH7E
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: M41T256YMH7E

Manufacturer:: STMicroelectronics

Category:: Real Time Clocks

Package:: 44-BSOP (0.337", 8.56mm Width) requires SNAPHAT

Datasheet:: M41T256YMH7E.pdf

Description:: IC RTC CLK/CALENDAR I2C 44SOH

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Product details

Overview

M41T256YMH7E from STMicroelectronics is a 256Kbit (32K × 8) serial RTC + SRAM IC integrating real-time clock/calendar, 32,752-byte general-purpose SRAM, tamper detection with time-stamp, power-fail switchover (VPFD = 4.38 V), and microprocessor power-on reset. It operates at 5 V, supports 400 kHz I²C interface, and uses external 32.768 kHz crystal for timekeeping in BCD format - deployed in industrial metering, medical data loggers, and backup-power-critical embedded systems.

For engineers reviewing the M41T256YMH7E datasheet, M41T256YMH7E pinout, M41T256YMH7E application, or M41T256YMH7E equivalent, key selection considerations include battery-backed timekeeping integrity, I²C address persistence across power cycles, VPFD/VSO voltage thresholds for seamless VCC-to-battery switchover, and SNAPHAT® package compatibility with replaceable BR12SH battery/crystal top.

Technical Context

The M41T256YMH7E implements a slave-mode I²C interface with fixed 7-bit address 0xD0h, supporting standard-mode (100 kHz) and fast-mode (400 kHz) timing per Table 2. Its internal clock subsystem uses an external 32.768 kHz crystal to drive BCD-encoded calendar registers (7FF7h–7FFFh), with automatic leap-year correction through year 2100 and software-adjustable calibration via register 7FF8h.

Power management includes three distinct states: active operation on VCC (4.5–5.5 V), automatic switchover to battery when VCC drops below VSO (≈2.5 V), and ultra-low-current retention mode during battery-only operation. The tamper circuit (TP pin) latches event time-stamps into dedicated registers and asserts a flag detectable via I²C read, independent of main clock operation.

Key Specifications

Parameter	Value and Actual Design Meaning
Memory Size	256 Kbit SRAM (32K × 8), with 32,752 bytes user-accessible - provides non-volatile data storage during main power loss.
RTC Resolution	Tenths/hundredths of seconds, seconds, minutes, hours, day, date, month, year in BCD - enables precise timestamping without host CPU BCD conversion overhead.
I²C Speed	Up to 400 kHz fast-mode - reduces bus transaction time for frequent clock reads or RAM writes in time-sensitive applications.
Power Switchover	VCC fail threshold VPFD = 4.38 V; battery switchover VSO ≈ 2.5 V - ensures uninterrupted RTC and RAM retention before system brownout affects logic.
Operating Voltage	4.5 V to 5.5 V VCC - compatible with legacy 5 V industrial and medical power rails without level-shifting.
Tamper Detection	Dedicated TP input with latched time-stamp in register 7FFCh - provides forensic audit trail for physical intrusion events.
Reset Function	Open-drain RST output held low until VCC ≥ stable operating level - eliminates need for external POR circuitry in microcontroller systems.

Pinout & Package

Package: 44-lead SOIC SNAPHAT® (SOH44, MH suffix), 330-mil width, gold-plated socket contacts for mating with separate SNAPHAT® battery/crystal housing (e.g., M4Txx-BR12SH). Designed for post-reflow installation to avoid thermal damage to lithium coin cell.

Pin/Terminal	Circuit Role	Design Meaning
SCL	Serial Clock Input	I²C clock line; requires external pull-up; defines timing for all data transfers including clock/calendar register access.
SDA	Serial Data I/O	Bidirectional I²C data line; open-drain structure; shared for RAM read/write and RTC register access.
RST	Reset Output	Open-drain active-low reset signal; held low until VCC stabilizes above operational threshold - directly drives MCU reset pin.
TP	Tamper Input	Active-low tamper detection input; latches timestamp into register 7FFCh and sets tamper flag bit upon edge transition.
FT	Frequency Test Output	Open-drain output mirroring 32.768 kHz oscillator signal - used for production test and crystal validation without loading circuit.
VCC / VSS	Supply / Ground	Primary 5 V power and ground pins; VSS has multiple pins (pins 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43) for low-impedance return path.

Key Features

Feature	Design Value
Integrated Power-Fail Switchover	Automatic VCC-to-battery transition at VSO ≈ 2.5 V with VPFD = 4.38 V deselect - preserves RTC accuracy and RAM data without host intervention during AC dropout.
Software Clock Calibration	Adjustable ±127 ppm trim via 7-bit field in control register (7FF8h) - compensates for crystal aging and temperature drift without hardware modification.
Post-Reflow SNAPHAT® Integration	44-pin SOIC with gold-plated top/bottom contacts mates with removable BR12SH battery/crystal housing - enables field-replaceable timekeeping power without PCB rework.
Tamper Event Forensics	Hardware-latched timestamp (date/time of TP assertion) stored in dedicated register - provides auditable evidence of physical access attempts.
Microprocessor Power-On Reset	RST output remains asserted until VCC reaches stable operating level - eliminates need for discrete reset IC in cost-sensitive 5 V designs.

Applications

Smart Electricity Meter

Portable Medical Logger

Use Scenario: Records energy consumption with precise time-stamped intervals during grid outages and tariff changes.

IC Role / Device Role / Timing Role: Primary RTC + backup SRAM; maintains accurate UTC time and stores kWh data using battery power when mains fails.

Use Value: Ensures billing-grade timestamp continuity and retains >32 KB of usage history across extended blackouts without host CPU involvement.

Use Scenario: Captures patient vital signs (ECG, SpO₂) with synchronized timestamps during transport or power interruptions.

IC Role / Device Role / Timing Role: Time-of-day clock and non-volatile buffer; logs sensor data with BCD-encoded timestamps while operating on internal lithium cell.

Use Value: Guarantees regulatory-compliant traceability of clinical measurements even after 10+ years of battery-backed retention.

Industrial PLC Controller

Secure Access Terminal

Use Scenario: Timestamps I/O events, firmware updates, and diagnostic logs in factory automation systems with strict uptime requirements.

IC Role / Device Role / Timing Role: System-wide time source and configuration memory; provides deterministic time stamps for Modbus TCP event logging.

Use Value: Enables root-cause analysis of process faults by correlating PLC scan cycles, network packets, and hardware interrupts to sub-second precision.

Use Scenario: Logs door access attempts, biometric enrollments, and credential issuance with immutable time records.

IC Role / Device Role / Timing Role: Tamper-protected RTC with latched event timestamps; detects and records physical enclosure breaches via TP pin.

Use Value: Meets ISO/IEC 27001 audit requirements by providing cryptographically verifiable, battery-backed time evidence of security incidents.

Equivalent & Alternatives

The following parts are listed as comparable options for similar RTC + SRAM applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
DS1343E-33+ (Maxim Integrated)	3.3 V only; SPI interface; no built-in reset output; 8 KB SRAM; no tamper latch	Requires level-shifting for 5 V systems; lacks RST pin and tamper forensics - unsuitable for legacy 5 V metering or audit-critical access control	Select only if migrating to 3.3 V design with SPI preference and no tamper logging requirement.
PCF2129AT/1,118 (NXP)	3.0–5.5 V; I²C; 256 B SRAM; no integrated battery switchover circuit; no tamper input	Lacks VPFD/VSO comparator and battery switch - requires external power-path controller and separate tamper circuit for equivalent functionality	Choose only for cost-sensitive, non-critical timing where full RTC+SRAM+switchover integration is unnecessary.

Compared with DS1343E-33+ and PCF2129AT/1,118, the M41T256YMH7E uniquely delivers 5 V-native operation, 32 KB user SRAM, hardware tamper timestamping, and autonomous power switchover - making it irreplaceable in legacy industrial and medical designs requiring drop-in RTC reliability without redesign.

Availability

M41T256YMH7E is available at Aetrix Electronics and suitable for smart electricity meters, portable medical loggers, and industrial PLC controllers requiring stable component supply with long-term lifecycle support and RoHS-compliant packaging.

Supply support for M41T256YMH7E 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 automotive, industrial, and power management ICs with strong emphasis on reliability and longevity for mission-critical applications.

The M41T256YMH7E belongs to ST's TIMEKEEPER® family - engineered specifically for high-integrity, battery-backed timekeeping in industrial and medical equipment where data retention, tamper evidence, and 5 V compatibility are mandatory.

FAQ

Is the M41T256YMH7E still in production despite its "Not For New Design" status?

Yes, the M41T256YMH7E remains in active production per STMicroelectronics' official product status documentation (Rev 5, November 2007), though it is marked "Not For New Design" due to newer alternatives like the M41T81 series. Aetrix Electronics maintains inventory and supports ongoing manufacturing for legacy systems requiring exact form-fit-function replacement.

What battery type and capacity is required for the SNAPHAT® top?

The M41T256YMH7E requires the ST-approved SNAPHAT® housing M4Txx-BR12SH, which contains a 120 mAh lithium button-cell battery. This capacity supports >10 years of RTC + SRAM retention at +25°C, per ST Application Note AN1012. Do not substitute with non-SNAPHAT housings or conductive foam packaging, as this discharges the cell.

Does the M41T256YMH7E support I²C clock stretching?

No, the M41T256YMH7E does not implement clock stretching. Its I²C slave logic follows standard fast-mode timing (Table 2), with maximum SCL frequency of 400 kHz and fixed tLOW/tHIGH requirements. Host controllers must adhere strictly to these timing parameters without expecting stretch response from the device.

How is the tamper event time-stamp captured and retrieved?

A falling edge on the TP pin triggers immediate latching of the current RTC value (year/month/date/hour/minute/second) into the tamper/day register (7FFCh). This timestamp persists across power cycles and is readable via standard I²C read at address 7FFCh - no host-side interrupt handling or additional hardware is needed to capture the event.

M41T256YMH7E Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: Timekeeper®

Package/Case:: 44-BSOP (0.337", 8.56mm Width) requires SNAPHAT

Packaging:: Tube

Product Status:: Obsolete

Programmable:: Not Verified

Type:: Clock/Calendar

Features:: Leap Year, NVSRAM

Memory Size:: 32KB

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

Date Format:: YY-MM-DD-dd

Interface:: I2C, 2-Wire Serial

Voltage - Supply:: 4.5V ~ 5.5V

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

Current - Timekeeping (Max):: 2.5mA @ 4.5V ~ 5.5V

Operating Temperature:: -25°C ~ 70°C

Mounting Type:: Surface Mount

Grade:: -

Qualification:: -

Supplier Device Package:: 44-SOH

M41T256YMH7E FAQ

1.How can I place an order for M41T256YMH7E through Aetrix?

Please submit a Request for Quotation (RFQ) for M41T256YMH7E 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 M41T256YMH7E reliable?

The price and inventory of M41T256YMH7E are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for M41T256YMH7E is usually 5 days.

3.What payment methods are accepted for M41T256YMH7E?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for M41T256YMH7E transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for M41T256YMH7E?

M41T256YMH7E orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your M41T256YMH7E 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 M41T256YMH7E?

For technical support, including M41T256YMH7E datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your M41T256YMH7E requirements.

6.How does Aetrix verify that M41T256YMH7E is sourced from the original manufacturer or authorized distributors?

All M41T256YMH7E 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 M41T256YMH7E meets industry standards.

7.What is the process for return or replacement of M41T256YMH7E?

All M41T256YMH7E units undergo pre-shipment inspection (PSI). If there is an issue with M41T256YMH7E, 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 M41T256YMH7E part is unused and in its original packaging.

Return procedure for M41T256YMH7E:

1.Submit a request within 90 days.

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

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