STC15W408AS-35I-SOP28 from STC Micro, in a SOP-28-300mil. 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	P2.6/CCP1_3	bidirectional	Standard I/O PORT2[6]. Alternate function CCP1_3: PCA/CCP capture, high-speed pulse output and PWM channel 1 (alternate mux group 3).
2	P2.7/CCP2_3	bidirectional	Standard I/O PORT2[7]. Alternate function CCP2_3: PCA/CCP capture, high-speed pulse output and PWM channel 2 (alternate mux group 3).
3	P1.0/ADC0/CCP1	bidirectional	Standard I/O PORT1[0]. Muxed with ADC channel 0 input and CCP1 (PCA capture / high-speed pulse output / PWM channel 1).
4	P1.1/ADC1/CCP0	bidirectional	Standard I/O PORT1[1]. Muxed with ADC channel 1 input and CCP0 (PCA capture / high-speed pulse output / PWM channel 0).
5	P1.2/ADC2/SS/ECI/CMPO	bidirectional	Standard I/O PORT1[2]. Alt-functions: ADC channel 2 input; SPI slave-select (SS); PCA external clock input (ECI); comparator output (CMPO).
6	P1.3/ADC3/MOSI	bidirectional	Standard I/O PORT1[3]. Muxed with ADC channel 3 input and SPI MOSI (master-out slave-in).
7	P1.4/ADC4/MISO	bidirectional	Standard I/O PORT1[4]. Muxed with ADC channel 4 input and SPI MISO (master-in slave-out).
8	P1.5/ADC5/SCLK	bidirectional	Standard I/O PORT1[5]. Muxed with ADC channel 5 input and SPI SCLK clock.
9	P1.6/ADC6/RxD_3/XTAL2/SysClkO_2	bidirectional	Standard I/O PORT1[6]. Muxed with ADC channel 6, UART RxD (mux group 3), external crystal output XTAL2, and system-clock output SysClkO_2 (SysClk/1, /2, /4).
10	P1.7/ADC7/TxD_3/XTAL1	bidirectional	Standard I/O PORT1[7]. Muxed with ADC channel 7, UART TxD (mux group 3), and external crystal input XTAL1 (or external clock input).
11	P5.4/RST/SysClkO/CMP-	bidirectional	Standard I/O PORT5[4]. Alt-functions: active-high external RESET input (RST, ISP-configurable); system-clock output SysClkO (SysClk/1, /2, /4); comparator negative input CMP- (set as high-Z input when used as comparator).
12	VCC	power_in	Positive supply. Operating range 2.4 V to 5.5 V. Decouple to GND with a 100 nF ceramic close to the pin.
13	P5.5/CMP+	bidirectional	Standard I/O PORT5[5]. Alt-function CMP+: comparator positive input (set the port to high-impedance input when used as CMP+).
14	GND	power_in	Ground / supply negative reference.
15	P3.0/RxD/INT4/T2CLKO	bidirectional	Standard I/O PORT3[0]. Muxed with UART RxD (primary), external interrupt INT4 (falling-edge only, supports power-down wake-up), and Timer2 clock output T2CLKO (via INT_CLKO[2]).
16	P3.1/TxD/T2	bidirectional	Standard I/O PORT3[1]. Muxed with UART TxD (primary) and Timer2 external clock input T2.
17	P3.2/INT0	bidirectional	Standard I/O PORT3[2]. External interrupt 0 (INT0): both edges when IT0=0, falling edge only when IT0=1. Supports power-down wake-up.
18	P3.3/INT1	bidirectional	Standard I/O PORT3[3]. External interrupt 1 (INT1): both edges when IT1=0, falling edge only when IT1=1. Supports power-down wake-up.
19	P3.4/T0/ECI_2	bidirectional	Standard I/O PORT3[4]. Muxed with Timer0 external clock input T0 and PCA external clock input ECI_2 (mux group 2).
20	P3.5/T0CLKO/CCP0_2	bidirectional	Standard I/O PORT3[5]. Alt-functions: Timer0 clock output T0CLKO (via INT_CLKO[0]) and CCP0 (mux group 2) capture / high-speed pulse output / PWM channel 0.
21	P3.6/INT2/RxD_2/CCP1_2	bidirectional	Standard I/O PORT3[6]. Alt-functions: external interrupt INT2 (falling-edge only, wake-from-power-down); UART RxD alternate mux group 2; CCP1 mux group 2.
22	P3.7/INT3/TxD_2/CCP2/CCP2_2	bidirectional	Standard I/O PORT3[7]. Alt-functions: external interrupt INT3 (falling-edge only, wake-from-power-down); UART TxD alternate mux group 2; CCP2 (primary) and CCP2_2 capture / high-speed pulse output / PWM channel 2.
23	P2.0/RSTOUT_LOW	bidirectional	Standard I/O PORT2[0]. After power-on and during reset the pin drives low (RSTOUT_LOW). Firmware may then drive it high or low; to read an external state, first set it high before reading.
24	P2.1/SCLK_2	bidirectional	Standard I/O PORT2[1]. Alt-function SPI SCLK on alternate mux group 2.
25	P2.2/MISO_2	bidirectional	Standard I/O PORT2[2]. Alt-function SPI MISO on alternate mux group 2.
26	P2.3/MOSI_2	bidirectional	Standard I/O PORT2[3]. Alt-function SPI MOSI on alternate mux group 2.
27	P2.4/ECI_3/SS_2	bidirectional	Standard I/O PORT2[4]. Alt-functions: PCA external clock input ECI mux group 3, and SPI slave-select SS mux group 2.
28	P2.5/CCP0_3	bidirectional	Standard I/O PORT2[5]. Alt-function CCP0 (mux group 3): PCA capture / high-speed pulse output / PWM channel 0.

Key specifications

Parameter	Value
Manufacturer	STC Micro
Package	SOP-28-300mil
Category	MCU
Pins	28

Ordering variants

Same part, different packaging or reel option.

STC15W408AS-35I-SOP28
STC15W408AS-35I-TSSOP28
STC15W408AS-35I-SKDIP28
STC15W408AS-35I-QFN28
STC15W408AS-35I-SOP20
STC15W408AS-35I-TSSOP20
STC15W408AS-35I-DIP20
STC15W408AS-35I-SOP16
STC15W408AS-35I-DIP16

CAD (KiCad official)

Symbol: STC15W408AS-35I-SOP28
Footprint: Package_SO:SOP-28_8.4x18.16mm_P1.27mm
3D model: SOP-28-300mil (KiCad packages3D, STEP)

3D model downloads

Two STEP files. Same geometry, different body top:

File	Size	Use it when
`stc15w408as-35i-sop28.step`	362 KB	You want the bare part, or you mark your own boards.
`stc15w408as-35i-sop28-etched.step`	5.2 MB	You want the part with `STC15W408AS-35I-SOP28` already on it.

The marking in the etched file is real recessed geometry cut into the solid, not a texture or a decal: 1252 faces against 447 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 (1219 pp, sha256 cc8c299c891646e0, 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