# STM8S903F3P6

**STMicroelectronics** · Microcontrollers (MCU/MPU/SOC) · TSSOP-20

STM8S903F3P6 from STMicroelectronics, in a TSSOP-20. Pinout and pin descriptions extracted from the manufacturer datasheet (extract_pins, cross-checked by a second model); symbol, footprint, and 3D from KiCad-official CAD.

## Pinout

| Pin | Name | Type | Function |
|---|---|---|---|
| 1 | PD4 | bidirectional | Port D4 is a high-sink-capable I/O (O3 speed) whose default function is Timer 5 channel 1 or the BEEP output, with UART1 clock (UART1_CK) available through the AFR2 remap option. |
| 2 | PD5 | bidirectional | Port D5 is a high-sink-capable I/O (O3 speed) whose default functions are analog input 5 (AIN5) and UART1 data transmit (UART1_TX). |
| 3 | PD6 | bidirectional | Port D6 is a high-sink-capable I/O (O3 speed) whose default functions are analog input 6 (AIN6) and UART1 data receive (UART1_RX). |
| 4 | NRST | bidirectional | Reset pin whose main function is Reset, listed as I/O in the pin table; its electrical limits are given in Table 44 (NRST pin characteristics), which is not in the extracted text. |
| 5 | PA1 | bidirectional | Port A1 is an I/O whose default function is the resonator/crystal input OSCIN, and in Halt/Active-halt mode it is automatically set to input weak pull-up, cannot wake the device, and should be used only as an input if Halt/Active-halt is used. |
| 6 | PA2 | bidirectional | Port A2 is an I/O whose default function is the resonator/crystal output OSCOUT, with slow output speed (O1, up to 2 MHz). |
| 7 | VSS | power_in | Digital ground. |
| 8 | VCAP | power_out | 1.8 V regulator capacitor pin that connects to the external VCAP capacitor described in section 10.3.1. |
| 9 | VDD | power_in | Digital power supply, specified for a 2.95 to 5.5 V operating voltage in the features list. |
| 10 | PA3 | bidirectional | Port A3 is a high-sink-capable I/O whose default function is Timer 5 channel 3, with SPI master/slave select (AFR1) or UART1 data transmit (AFR1:0) available through remap options. |
| 11 | PB5 | bidirectional | Port B5 is a true open-drain I/O (no P-buffer, weak pull-up or protection diode to VDD) carrying I2C data, with Timer 1 break input (TIM1_BKIN) available through the AFR4 remap. |
| 12 | PB4 | bidirectional | Port B4 is a true open-drain I/O (no P-buffer, weak pull-up or protection diode to VDD) carrying I2C clock, with ADC external trigger (ADC_ETR) available through the AFR4 remap. |
| 13 | PC3 | bidirectional | Port C3 is a high-sink-capable I/O whose default function is Timer 1 channel 3, with top level interrupt (TLI, AFR3) and Timer 1 inverted channel 1 (AFR7) available through remap options. |
| 14 | PC4 | bidirectional | Port C4 is a high-sink-capable I/O whose default function is Timer 1 channel 4 or configurable clock output (CLK_CCO), with analog input 2 (AIN2, AFR2) and Timer 1 inverted channel 2 (AFR7) available through remap options. |
| 15 | PC5/SPI_SCK | bidirectional | Port C5 is a high-sink-capable I/O whose default function is SPI clock, with Timer 5 channel 1 available through the AFR0 remap. |
| 16 | PC6 | bidirectional | Port C6 is a high-sink-capable I/O whose default function is SPI master out/slave in, with Timer 1 channel 1 available through the AFR0 remap. |
| 17 | PC7 | bidirectional | Port C7 is a high-sink-capable I/O whose default function is SPI master in/slave out, with Timer 1 channel 2 available through the AFR0 remap. |
| 18 | PD1/SWIM | bidirectional | Port D1 is a high-sink-capable I/O (O4 speed) carrying the SWIM data interface; it is in input pull-up during reset and after internal reset release. |
| 19 | PD2 | bidirectional | Port D2 is a high-sink-capable I/O whose default function is analog input 3 (AIN3), with Timer 5 channel 3 available through the AFR1 remap. |
| 20 | PD3 | bidirectional | Port D3 is a high-sink-capable I/O whose default function is analog input 4 (AIN4), with Timer 5 channel 2 and ADC external trigger (ADC_ETR) listed as its other function. |

## Key specifications

| Parameter | Value |
|---|---|
| Manufacturer | STMicroelectronics |
| Package | TSSOP-20 |
| Category | Embedded Processors & Controllers |
| Pins | 20 |

## CAD (KiCad official)

- Symbol: `STM8S903F3P6`
- Footprint: `Package_SO:TSSOP-20_4.4x6.5mm_P0.65mm`
- 3D model: TSSOP-20 (KiCad packages3D, STEP)
- 3D model files: `stm8s903f3p6-etched.step` / `stm8s903f3p6-etched.glb` carry the MPN laser-etched on the die in a toggleable `Adom.LaserEtch` group (Fusion-ready); `stm8s903f3p6.step` / `stm8s903f3p6.glb` are the bare package body.

## Provenance

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

- **Datasheet:** [STMicroelectronics datasheet](https://jlcpcb.com/api/file/downloadByFileSystemAccessId/8588922932042584064) (124 pp, sha256 `76ef2064c8429253`, retrieved 2026-10-08, tier: lcsc)
- **Extractor:** parts-factory `2.0.0` / `extract_pins 0.3`, primary `claude-haiku-5-5` (text), consensus `claude-sonnet-5-5` (agreed), guards: pin_guards 0.1: passed. Pins are checked against the footprint pad set and their cited datasheet pages before publish.
- **CAD:** KiCad official libraries (CC-BY-SA 4.0).

[Datasheet PDF](docs/stm8s903f3p6-datasheet.pdf)