STM8L101F1U6ATR from STMicroelectronics, in a UFQFPN-20(3x3). 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	NRST/PA1	bidirectional	Active-low reset input with internal pull-up at power-up; can be reconfigured as general-purpose I/O PA1 (push-pull output only, not open-drain and not input) via option byte. High-sink capable (20 mA).
2	PA2	bidirectional	General-purpose I/O port A bit 2. Supports floating or weak pull-up input, external interrupt, open-drain or push-pull output, and 20 mA high sink/source drive.
3	PA6/COMP_REF	bidirectional	General-purpose I/O port A bit 6, alternate function is COMP_REF, the external voltage reference input shared by comparators COMP1 and COMP2. High-sink/source (20 mA) capable, with weak pull-up and external interrupt support.
4	VSS	power_in	Digital ground return for the device (0 V reference).
5	VDD	power_in	Main supply voltage input. Operating range 1.65 V to 3.6 V. Powers core and I/Os; an on-chip regulator derives the internal 1.8 V rail.
6	PD0/TIM3_CH2/COMP1_CH3	bidirectional	General-purpose I/O port D bit 0. Alternate functions: TIM3 channel 2 (input capture / output compare / PWM) or COMP1 channel 3 analog input. 20 mA high-sink/source capable.
7	PB0/TIM2_CH1/COMP1_CH1	bidirectional	General-purpose I/O port B bit 0. Alternate functions: TIM2 channel 1 or COMP1 channel 1 analog input. 20 mA high-sink/source drive.
8	PB1/TIM3_CH1/COMP1_CH2	bidirectional	General-purpose I/O port B bit 1. Alternate functions: TIM3 channel 1 or COMP1 channel 2 analog input. 20 mA high-sink/source drive.
9	PB2/TIM2_CH2/COMP2_CH1	bidirectional	General-purpose I/O port B bit 2. Alternate functions: TIM2 channel 2 or COMP2 channel 1 analog input. 20 mA high-sink/source drive.
10	PB3/TIM2_ETR/COMP2_CH2	bidirectional	General-purpose I/O port B bit 3. Alternate functions: TIM2 external trigger input or COMP2 channel 2 analog input. 20 mA high-sink/source drive.
11	PB4/SPI_NSS	bidirectional	SPI master/slave select (NSS), or general-purpose port B bit 4. 20 mA high-sink/source drive; supports open-drain or push-pull output.
12	PB5/SPI_SCK	bidirectional	SPI clock (SCK), or general-purpose port B bit 5. 20 mA high-sink/source drive.
13	PB6/SPI_MOSI	bidirectional	SPI master-out/slave-in data (MOSI), or general-purpose port B bit 6. 20 mA high-sink/source drive.
14	PB7/SPI_MISO	bidirectional	SPI master-in/slave-out data (MISO), or general-purpose port B bit 7. 20 mA high-sink/source drive.
15	PC0/I2C_SDA	bidirectional	I2C serial data (SDA). True open-drain I/O (no P-buffer, no weak pull-up, no protection diode to VDD) - external pull-up to VDD required. Also usable as general-purpose port C bit 0.
16	PC1/I2C_SCL	bidirectional	I2C serial clock (SCL). True open-drain I/O (no P-buffer, no weak pull-up, no protection diode to VDD) - external pull-up to VDD required. Also usable as general-purpose port C bit 1.
17	PC2/USART_RX	bidirectional	USART receive data (RX), or general-purpose port C bit 2. 20 mA high-sink/source drive.
18	PC3/USART_TX	bidirectional	USART transmit data (TX), or general-purpose port C bit 3. 20 mA high-sink/source drive.
19	PC4/USART_CK/CCO	bidirectional	USART synchronous clock (CK) or configurable clock output (CCO), or general-purpose port C bit 4. 20 mA high-sink/source drive.
20	PA0/SWIM/BEEP/IR_TIM	bidirectional	SWIM single-wire debug/programming interface (primary function after reset), beeper output (BEEP), and infrared timer output (IR_TIM). Also usable as GPIO PA0. PA0 has the LED-driver high-sink capability enabled via IR_CR register. Input pull-up during and after reset release.

Key specifications

Parameter	Value
Manufacturer	STMicroelectronics
Package	UFQFPN-20(3x3)
Category	Embedded Processors & Controllers
Pins	20

Ordering variants

Same part, different packaging or reel option.

STM8L101F1U6ATR
STM8L101F1U6ATRF2U6ATR
STM8L101F1U6ATRF3U6ATR
STM8L101F1U6TR
STM8L101F1U6ATRF2U6TR
STM8L101F1U6ATRF3U6TR
STM8L101F1U6ATRF2T6TR
STM8L101F1U6ATRF3T6TR
STM8L101F1U6ATRG2U6TR
STM8L101F1U6ATRG3U6TR
STM8L101F1U6ATRG2U6ATR
STM8L101F1U6ATRG3U6ATR
STM8L101F1U6ATRK3U6TR
STM8L101F1U6ATRK3T6TR

CAD (KiCad official)

Symbol: STM8L101F1U6ATR
Footprint: Package_DFN_QFN:ST_UFQFPN-20_3x3mm_P0.5mm
3D model: UFQFPN-20(3x3) (KiCad packages3D, STEP)

Provenance

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

Datasheet: STMicroelectronics datasheet (None pp, sha256 c8e0b0d1f3c75a46, retrieved 2026-08-17, tier: lcsc)
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