STMicroelectronics M48T86MH1E

Overview

M48T86MH1E from STMicroelectronics is a 5.0 V real-time clock (RTC) with integrated lithium battery and 32.768 kHz crystal in a self-contained SOH28 SNAPHAT® package. It provides non-volatile timekeeping (seconds to years with leap-year compensation), 114 bytes of battery-backed RAM, three software-maskable interrupts (alarm, periodic, update-ended), and programmable square-wave output up to 500 ms period - deployed in legacy PC motherboards and industrial control panels for time-stamped logging.

For engineers reviewing the M48T86MH1E datasheet, M48T86MH1E pinout, M48T86MH1E application, or M48T86MH1E equivalent, key selection criteria include Intel/Motorola bus timing selectability, VCC power-fail protection threshold (VPFD), IRQ open-drain drive capability, SQW frequency programmability via Register A, and SNAPHAT® top-mount mechanical compatibility with surface-mount reflow processes.

Technical Context

The M48T86MH1E implements a binary-coded decimal (BCD) real-time clock with automatic leap-year compensation across a 100-year range, driven by an internal 32.768 kHz quartz oscillator tested to ±23 ppm at 25°C (±1 minute/month accuracy). Its dual-bus interface supports Intel-style (AS/DS strobes) and Motorola-style (MOT-selectable) timing protocols, enabling drop-in replacement in legacy x86 systems.

Interrupt logic is fully register-controlled: Register B enables/disables alarm (AIE), periodic (PIE), and update-ended (UIE) interrupts; Register C flags (AF/PF/UF/IRQF) are cleared only on Register C read or RST assertion. The IRQ output is open-drain and requires external pull-up; SQW output is disabled when VCC falls below VPFD and is controlled by SQWE bit (Register B, bit 3).

Key Specifications

Pinout & Package

SOH28 package: 28-pin plastic small-outline IC with dual-row gold-plated sockets for mating with SNAPHAT® top housing containing battery and crystal. Mechanical outline per ST document Table 16 (page 30); SNAPHAT® insertion is keyed to prevent reverse mounting and occurs post-reflow to avoid thermal damage.

Key Features

Applications

Equivalent & Alternatives

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

Compared with DS12887AN+ and bq3287, the M48T86MH1E uniquely combines SOIC SMT compatibility with field-replaceable SNAPHAT® battery/crystal - preserving legacy register behavior while enabling modern assembly flow and long-term serviceability.

Availability

M48T86MH1E is available at Aetrix Electronics and suitable for PC motherboard timekeeping, industrial data loggers, POS terminal clock backup, and medical device event logging requiring stable component supply and long-lifecycle support.

Supply support for M48T86MH1E 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, analog ICs, MEMS, and power devices for automotive, industrial, and consumer markets.

The M48T86 belongs to ST's legacy real-time clock product line, engineered specifically for backward-compatible PC and industrial timing applications requiring integrated battery-backed timekeeping and non-volatile RAM in standardized footprints.

FAQ

What is the function of the RCL pin on the M48T86MH1E?

The RCL (RAM Clear) pin clears all 114 bytes of general-purpose non-volatile RAM to 0xFF when held low for ≥100 ms while the oscillator is running. It does not affect clock registers, control bits, or battery load. This function is only active when VCC is applied and is used for secure RAM initialization without altering timekeeping state.

How does the M48T86MH1E handle power failure during operation?

When VCC drops below the power-fail deselect voltage (VPFD ≈ 4.0 V), the M48T86MH1E automatically disables bus access and enters battery-backup mode. The internal lithium cell maintains clock operation and RAM retention for up to 10 years. Upon power restoration, a 200 ms stabilization delay prevents register corruption until VCC is stable and a valid system reset can be issued.

Can the M48T86MH1E operate with both 3.3 V and 5.0 V host systems?

No - the M48T86MH1E is strictly a 5.0 V device. Its VCC specification is 4.5–5.5 V, and all I/O pins (AD0–AD7, IRQ, SQW, etc.) are designed for 5 V TTL/CMOS logic levels. Interfacing with 3.3 V systems requires level-shifting circuitry; it does not support mixed-voltage operation or 3.3 V tolerant inputs.

What is the purpose of the SNAPHAT® top housing, and is it included with M48T86MH1E?

The SNAPHAT® top housing (e.g., M4T28-BR12SH) contains the lithium battery and 32.768 kHz crystal and mounts onto the SOH28 package after PCB reflow. It is not included with M48T86MH1E - the SOIC and SNAPHAT® are ordered separately. This modular design prevents thermal damage to the battery/crystal during soldering and allows field replacement of the power source.