M41T81SM6F from STMicroelectronics, in a SOIC-8. Pinout and pin descriptions extracted from the manufacturer datasheet by ds2sf; symbol, footprint, and 3D from KiCad-official CAD.

Pinout

Pin	Name	Type	Function
1	XI	input	32.768 kHz crystal oscillator input. Connect to one terminal of an external 32.768 kHz tuning-fork crystal (integrated load capacitance ~12.5 pF).
2	XO	output	32.768 kHz crystal oscillator output. Connect to the other terminal of the external 32.768 kHz crystal.
3	VBAT	power_in	Battery supply voltage input. Connect to a lithium button cell (typ 3 V) to provide non-volatile clock operation when VCC is removed. The device automatically switches to VBAT when VCC falls below the switchover threshold (VSO).
4	VSS	power_in	Ground / 0 V reference for both VCC and VBAT domains.
5	SDA	bidirectional	I2C serial data (open-drain, bidirectional). Requires an external pull-up resistor to VCC. Supports 400 kHz Fast-mode I2C. Slave address D0h.
6	SCL	input	I2C serial clock input from the bus master. Requires an external pull-up resistor to VCC. Supports up to 400 kHz.
7	/IRQ/FT/OUT/SQW	output	Multi-function open-drain output. Selectable via register bits as: active-low interrupt request (alarm / watchdog / oscillator-fail), frequency test output, general-purpose output driver, or programmable square-wave (1 Hz-32.768 kHz). Requires external pull-up. Square wave has the highest priority when SQWE is enabled.
8	VCC	power_in	Main supply voltage input, 2.7 V to 5.5 V. Continuously monitored against VPFD (2.5-2.7 V) and VSO for automatic power-fail detection and battery switchover.

Key specifications

Parameter	Value
Manufacturer	STMicroelectronics
Package	SOIC-8
Category	RTC
Pins	8

Ordering variants

Same part, different packaging or reel option.

M41T81SM6FM6E
M41T81SM6F
M41T81SM6FMY6E
M41T81SM6FMY6F

CAD (KiCad official)

Symbol: M41T81SM6F
Footprint: Package_SO:SOIC-8_3.9x4.9mm_P1.27mm
3D model: SOIC-8 (KiCad packages3D, STEP)

3D model downloads

Two STEP files. Same geometry, different body top:

File	Size	Use it when
`m41t81sm6f.step`	122 KB	You want the bare part, or you mark your own boards.
`m41t81sm6f-etched.step`	1.9 MB	You want the part with `M41T81SM6F` already on it.

The marking in the etched file is real recessed geometry cut into the solid, not a texture or a decal: 495 faces against 147 in the bare model. It survives export, section views, and rendering in any CAD tool, and it drops straight into KiCad or Fusion with no extra setup.

Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

Datasheet: STMicroelectronics datasheet (32 pp, sha256 791596b091730dfd, retrieved 2026-08-17, tier: manufacturer)
Extractor: ds2sf (Claude). Every pin and dimension is cited to a datasheet page; it refuses to fabricate.
CAD: KiCad official libraries (CC-BY-SA 4.0).

Datasheet PDF