STM32
STM32F103C8T6 "Blue Pill"
Generic STM32F103C8T6 breakout — 72MHz Cortex-M3, 3.3V logic, most GPIOs 5V-tolerant, notoriously inconsistent clone quality.
STM32F103C8T6 · Generic / various (STMicroelectronics chip)
Overview
The "Blue Pill" isn't a single manufacturer's product — it's a generic PCB design built around ST's STM32F103C8T6 (Cortex-M3, 72MHz) that's been cloned by dozens of factories for years, so board-level details vary. Many boards ship with a non-compliant PA12 (USB D+) pull-up, which can make USB device firmware enumerate unreliably. That is separate from the factory ROM boot path: ST documents USART1 for this medium-density device, not USB DFU. Use SWD/ST-Link for the most reliable programming route, or BOOT0 plus USART1 when using the system-memory bootloader. PA11/PA12 are marked FT in ST's pin table, but USB operation must still obey USB electrical levels.
Wiring tip: flash reliably via the 4-pin SWD header (ST-Link); the factory system-memory bootloader uses USART1, not USB DFU
Ecosystem: stm32
Pins & wiring
Logical two-sided map — confirm the package or board drawing before wiring.
All pins
Hover · click to selectSelected pin
3V3
- Direction
- Power
- Logic / rail
- 3.3 V
Full pin table
| Name | Role | Direction | Voltage | Note |
|---|---|---|---|---|
| Power | Power | 3.3 V | — | |
| Power | Power | — | USB 5V / external 5V input to the onboard regulator. | |
| Ground | Passive | — | — | |
| Power | Power | — | Powers the RTC/backup registers when main power is off. Tie to a coin cell (via a diode) if you need the RTC to keep time on power loss, otherwise tie to 3V3. | |
| Control | In | — | Active-low external reset. | |
| Control | In | — | Pull HIGH before reset to enter the system-memory bootloader (USART1 on this device); LOW boots user flash. | |
| Analog | Bidirectional | 3.3 V | ||
| Analog | Bidirectional | 3.3 V | ||
| UART | Bidirectional | 3.3 V | ||
| UART | Bidirectional | 3.3 V | ||
| SPI | Bidirectional | 3.3 V | ||
| SPI | Bidirectional | 3.3 V | ||
| SPI | Bidirectional | 3.3 V | ||
| SPI | Bidirectional | 3.3 V | ||
| GPIO | Bidirectional | 3.3 V | ||
| UART | Bidirectional | 3.3 V | ||
| UART | Bidirectional | 3.3 V | ||
| USB | Bidirectional | 3.3 V | USB D-. Marked FT (5V-tolerant as GPIO) in ST's pin table; USB mode still requires USB-compliant signalling. | |
| USB | Bidirectional | 3.3 V | USB D+. Marked FT as GPIO. Clone boards may fit the wrong USB pull-up value, affecting user-firmware enumeration. | |
| Control | Bidirectional | 3.3 V | SWD debug data. Avoid repurposing if you want to keep using an ST-Link. | |
| Control | Bidirectional | 3.3 V | SWD debug clock. Avoid repurposing if you want to keep using an ST-Link. | |
| GPIO | Bidirectional | 3.3 V | ||
| Analog | Bidirectional | 3.3 V | ||
| Analog | Bidirectional | 3.3 V | ||
| GPIO | Bidirectional | 3.3 V | Also BOOT1 — sampled at reset together with BOOT0 to select the boot source; some boards mark this pin's header position accordingly. | |
| SPI | Bidirectional | 3.3 V | ||
| SPI | Bidirectional | 3.3 V | ||
| SPI | Bidirectional | 3.3 V | ||
| I2C | Bidirectional | 3.3 V | ||
| I2C | Bidirectional | 3.3 V | ||
| I2C | Bidirectional | 3.3 V | ||
| I2C | Bidirectional | 3.3 V | ||
| I2C | Bidirectional | 3.3 V | ||
| I2C | Bidirectional | 3.3 V | ||
| SPI | Bidirectional | 3.3 V | ||
| SPI | Bidirectional | 3.3 V | ||
| SPI | Bidirectional | 3.3 V | ||
| SPI | Bidirectional | 3.3 V | ||
| GPIO | Bidirectional | 3.3 V | Drives the onboard LED (active-LOW) on nearly every Blue Pill variant. Port C pins have lower max drive current than Port A/B on this chip — don't expect them to sink/source as much for an external LED/relay. | |
| GPIO | Bidirectional | 3.3 V | Shared with the 32.768kHz RTC crystal oscillator if one is fitted. | |
| GPIO | Bidirectional | 3.3 V | Shared with the 32.768kHz RTC crystal oscillator if one is fitted. |
Wiring examples
Power-up and flashing
Any 3.3V hostPowers from Micro-USB with no extra wiring. Program reliably over SWD/ST-Link, or enter the factory system-memory bootloader and use USART1; this MCU's ROM does not provide USB DFU.
| STM32F103C8T6 "Blue Pill" pin | Connects to | Note |
|---|
- The clone-board PA12 pull-up issue affects USB device firmware; it does not create a ROM USB DFU path. SWD (PA13/PA14 + 3V3/GND) sidesteps the board's USB circuitry.
- PA11/PA12 are marked FT when used as GPIO, but never apply 5V while they are configured for USB signalling.
- Set BOOT0 HIGH before reset to enter the USART1 system-memory bootloader; LOW runs user flash.
Specifications
Electrical
Interface
Physical
- USB Connector
- micro-usbsrc
- Package
- Breakout Board
- Length
- Varies by vendor
- Mounting
- tht
- Header Format
- custom
Footprint
No independently verified physical footprint is on file for this part yet.
Alternatives
Upgrades
Strictly better on the headline spec, but expect to touch firmware or wiring to actually use the difference.
Adds WiFi/Bluetooth and a much simpler, consistent flashing story (no USB pull-up lottery) for a similar price.
Compare with STM32F103C8T6 "Blue Pill"- Wi-Fi: no → yes
- Core: ARM Cortex-M3 → Xtensa dual-core LX6
Similar parts
Does the same job with a different part. Expect wiring and library changes — a starting point, not a guarantee.
Much simpler toolchain for beginners (stock Arduino IDE, no ST-Link/DFU questions) at the cost of a slower 8-bit core.
Compare with STM32F103C8T6 "Blue Pill"- Core: ARM Cortex-M3 @ 72MHz → AVR 8-bit @ 16MHz
Documents
Datasheets
- STM32F103x8 / STM32F103xB DatasheetSTMicroelectronics
Frequently asked questions
What voltage does the STM32F103C8T6 "Blue Pill" run at?
The STM32F103C8T6 "Blue Pill" runs at 3.3V, per the spec sheet below. Always double-check against the specific board you have — some breakouts add an onboard regulator that changes the usable input range.
How many pins does the STM32F103C8T6 "Blue Pill" have?
The STM32F103C8T6 "Blue Pill" has 41 pins, communicating over CAN, I2C, SPI, UART, USB. See the full pinout table in Pins & wiring for each pin's role.
Can I simulate the STM32F103C8T6 "Blue Pill" before ordering hardware?
Not yet — the STM32F103C8T6 "Blue Pill" does not have a live simulation model in Banana Board today, so validate the wiring here and test on real hardware.
Where is the STM32F103C8T6 "Blue Pill" datasheet?
Linked in the Documents section on this page, and cited on every spec that came from it.
Related references
Build it, do not just look it up
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