STMicroelectronics M41T256YMH7F

Overview

M41T256YMH7F from STMicroelectronics is a 256Kbit (32K × 8) serial RTC with integrated 32.768kHz crystal oscillator interface, I²C-compatible 400kHz serial interface, 32,752-byte general-purpose SRAM, tamper-detection circuit with time-stamp, and microprocessor power-on reset function - used in industrial metering, legacy POS terminals, and backup-critical embedded controllers requiring long-term timekeeping under main power loss.

For engineers reviewing the M41T256YMH7F datasheet, M41T256YMH7F pinout, M41T256YMH7F application, or M41T256YMH7F equivalent, key selection considerations include VCC switchover threshold (VPFD = 4.2–4.5V), battery-backed clock/calendar BCD register map (7FF7h–7FFFh), SNAPHAT® SOIC-44 mechanical compatibility, and tamper event timestamping capability.

Technical Context

The M41T256YMH7F integrates a real-time clock/calendar, 32.752-byte SRAM, and power-fail detection in a single IC. Its I²C slave interface uses fixed address 0xD0h, supports automatic address incrementing, and operates up to 400kHz with tSU:DAT ≥ 100ns and tHD:STA ≥ 600ns timing compliance.

It implements dual power domains: VCC (4.5–5.5V) for active operation and VBAT (lithium button cell) for data retention. Power switchover triggers at VPFD (4.2–4.5V) and full battery takeover occurs below VSO; tamper detection latches events with timestamped register updates in BCD format across year/month/date/hour/minute/second/tenths-hundredths.

Key Specifications

Pinout & Package

The M41T256YMH7F is housed in a 44-lead plastic small outline SNAPHAT® package (SOH44, MH variant), featuring gold-plated socket contacts at both ends to interface with the removable SH-series battery/crystal housing. The package enables post-reflow installation of the lithium coin-cell and crystal assembly, avoiding thermal damage during SMT reflow.

Key Features

Applications

Equivalent & Alternatives

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

Compared with DS1343E-33+ and PCF2129AT/1,118, the M41T256YMH7F uniquely combines 32KB user SRAM, tamper-input with hardware timestamping, and SNAPHAT® field-serviceable battery/crystal - making it irreplaceable in legacy industrial systems requiring long-term data integrity and physical security.

Availability

M41T256YMH7F is available at Aetrix Electronics and suitable for smart energy metering, legacy point-of-sale terminals, and industrial PLC backups requiring stable component supply and long-term lifecycle support.

Supply support for M41T256YMH7F 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 sensor solutions for industrial, automotive, and consumer markets.

The M41T256YMH7F belongs to ST's TIMEKEEPER® family - engineered specifically for high-reliability, battery-backed timekeeping and data retention in mission-critical industrial and metering applications where firmware independence and hardware-level tamper evidence are mandatory.

FAQ

What is the purpose of the FT pin on the M41T256YMH7F?

The FT (Frequency Test) pin is an open-drain output that provides the internal 32.768kHz oscillator signal for external validation. It allows engineers to monitor crystal stability, verify oscillator startup, and diagnose timing faults without accessing internal registers - critical during production test and field calibration.

How does the tamper detection circuit operate and where is the timestamp stored?

The TP (Tamper) pin is an active-low input that triggers hardware latching of the current BCD time into the Tamper/Day register (7FFCh). This timestamp is preserved across power cycles and cannot be overwritten by software - ensuring immutable forensic evidence of physical intrusion events.

Can the M41T256YMH7F operate without an external crystal?

No - the M41T256YMH7F requires an external 32.768kHz tuning-fork crystal connected to its X1/X2 pins (not shown in pin table but defined in Figure 3 block diagram). The oscillator circuit is not self-contained; crystal accuracy directly determines timekeeping precision and must meet specified load capacitance and ESR limits per Table 9.

What is the role of the SNAPHAT® housing and why is it shipped separately?

SNAPHAT® is a removable 4-pin top housing containing a 120mAh lithium battery and crystal, mechanically keyed to mate with the SOH44 SOIC base. It ships separately to avoid exposing the battery to reflow soldering temperatures (>200°C), which would degrade capacity and safety - enabling safe surface-mount assembly followed by manual snap-on integration.