STC8H3K64S2-45I-TSSOP20 from STC Micro, in a TSSOP-20. 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	P1.0/ADC0/RxD2/PWM1P	bidirectional	Standard I/O P1.0; muxed with ADC channel 0 input, UART2 receive (RxD2), and PWM1 positive capture/output (PWM1P). Power-on state is high-impedance input (must be configured before use).
2	P1.6/ADC6/RxD_3/PWM4P/MCLKO_2/XTALO	bidirectional	Standard I/O P1.6; muxed with ADC channel 6, UART1 receive alt-3 (RxD_3), PWM4 positive output, master clock divided output (MCLKO_2), and external crystal output (XTALO).
3	P1.7/ADC7/TxD_3/PWM4N/PWM5_2/XTALI	bidirectional	Standard I/O P1.7; muxed with ADC channel 7, UART1 transmit alt-3 (TxD_3), PWM4 negative output, PWM5 capture/output alt-2, and external crystal/clock input (XTALI).
4	AGnd	power_in	ADC analog ground reference. Should be tied to the system ground plane at a single point near the MCU for best analog performance.
5	ADC_VRef+	power_in	ADC external positive reference input, 2.4 V to MCU-VCC. Must be tied to an external reference (or AVcc for low-precision applications); leaving floating produces leakage current.
6	AVcc	power_in	ADC analog supply pin (1.9 V to 5.5 V, matched to VCC). Decouple with 0.1 uF close to the pin.
7	P5.4/nRST/MCLKO/SS_3/PWM6_2	bidirectional	Standard I/O P5.4; muxed with active-low external reset (nRST), master clock output (MCLKO), SPI slave-select alt-3 (SS_3), and PWM6 capture/output alt-2. Default at factory is P5.4 I/O; nRST function must be enabled via ISP option, which takes effect after a power cycle.
8	Vcc	power_in	Main digital supply pin, 1.9 V to 5.5 V. Bulk decoupling of 10 uF plus 0.1 uF between Vcc and Gnd is recommended, placed close to the chip.
9	P5.5	bidirectional	Standard general-purpose I/O port pin P5.5. Power-on state is high-impedance input; configure the port mode register before use.
10	Gnd	power_in	Digital ground return for the main Vcc rail.
11	P3.0/RxD/INT4	bidirectional	Standard I/O P3.0; muxed with UART1 receive (RxD) and external interrupt 4 (INT4). Also used together with P3.1/P3.2 by the mask-ROM bootloader to detect USB-ISP entry at reset.
12	P3.1/TxD	bidirectional	Standard I/O P3.1; muxed with UART1 transmit (TxD). Powers up in weak pull-up (quasi-bidirectional) mode.
13	P3.2/INT0/SCLK_4/SCL_4/PWMETI/PWMETI2	bidirectional	Standard I/O P3.2; muxed with external interrupt 0 (INT0), SPI clock alt-4 (SCLK_4), I2C clock alt-4 (SCL_4), and PWM external trigger inputs (PWMETI, PWMETI2).
14	P3.3/INT1/MISO_4/SDA_4/PWM4N_4/PWM7_2	bidirectional	Standard I/O P3.3; muxed with external interrupt 1 (INT1), SPI MISO alt-4, I2C SDA alt-4, PWM4 negative output alt-4, and PWM7 capture/output alt-2.
15	P3.4/T0/T1CLKO/MOSI_4/PWM4P_4/PWM8_2/CMPO	bidirectional	Standard I/O P3.4; muxed with Timer 0 external clock input (T0), Timer 1 divided clock output (T1CLKO), SPI MOSI alt-4, PWM4 positive output alt-4, PWM8 capture/output alt-2, and analog comparator output (CMPO).
16	P3.5/T1/T0CLKO/SS_4/PWMFLT	bidirectional	Standard I/O P3.5; muxed with Timer 1 external clock input (T1), Timer 0 divided clock output (T0CLKO), SPI slave-select alt-4 (SS_4), and enhanced-PWM external fault input (PWMFLT).
17	P3.6/INT2/RxD_2/CMP-	bidirectional	Standard I/O P3.6; muxed with external interrupt 2 (INT2), UART1 receive alt-2 (RxD_2), and the analog comparator negative input (CMP-).
18	P3.7/INT3/TxD_2/CMP+	bidirectional	Standard I/O P3.7; muxed with external interrupt 3 (INT3), UART1 transmit alt-2 (TxD_2), and the analog comparator positive input (CMP+).
19	P1.2/ADC2/PWM2P/SS/T2	bidirectional	Standard I/O P1.2; muxed with ADC channel 2, PWM2 positive capture/output (PWM2P), SPI slave-select (SS), and Timer 2 external clock input (T2).
20	P1.1/ADC1/TxD2/PWM1N	bidirectional	Standard I/O P1.1; muxed with ADC channel 1, UART2 transmit (TxD2), and PWM1 negative output (PWM1N).

Key specifications

Parameter	Value
Manufacturer	STC Micro
Package	TSSOP-20
Category	MCU
Pins	20

Ordering variants

Same part, different packaging or reel option.

STC8H3K64S2-45I-TSSOP20
STC8H3K64S2-45I-LQFP48
STC8H3K64S2-45I-QFN48
STC8H3K64S2-45I-LQFP32
STC8H3K64S2-45I-QFN32
STC8H3K64S2-45I-PDIP40

CAD (KiCad official)

Symbol: STC8H3K64S2-45I-TSSOP20
Footprint: Package_SO:TSSOP-20_4.4x6.5mm_P0.65mm
3D model: TSSOP-20 (KiCad packages3D, STEP)

3D model downloads

Two STEP files. Same geometry, different body top:

File	Size	Use it when
`stc8h3k64s2-45i-tssop20.step`	267 KB	You want the bare part, or you mark your own boards.
`stc8h3k64s2-45i-tssop20-etched.step`	5.0 MB	You want the part with `STC8H3K64S2-45I-TSSOP20` already on it.

The marking in the etched file is real recessed geometry cut into the solid, not a texture or a decal: 1215 faces against 327 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: STC Micro datasheet (2180 pp, sha256 046aea020e4685f3, retrieved 2026-08-17, tier: lcsc)
Datasheet language: Chinese. Pin names, descriptions, and specs on this page were extracted and translated to English by ds2sf; the linked PDF is the manufacturer original.
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