ARM Cortex M3 STM32F103C8T6

It’s amazing what you can get in a microcontroller board these days for just over $2. For example, just search ebay.com or alibaba.com for the key word ‘STM32F103C8T6’.  You will see the links to an ARM Cortex M3 STM32F103C8T6 development board for just over $2 US including shipping (usually from China, so it may take a bit to arrive). If you want it faster (if you live in the U.S.), you can order from US suppliers but expect to pay more.

The board, sometimes called the ‘blue pill‘ (a reference to the 2016 film “The Matrix”) looks like this:

ARM processors are based on the RISC (reduced instruction set computer) architecture developed by Advanced RISC Machines (ARM). ARM licenses the technology to manufacturers such as STMicroelectronics which makes the processor on this particular board. The processor data sheet can be downloaded HERE. The reference manual is HERE. The programming manual is HERE. The system memory boot mode application note is HERE.

Briefly, here are the specifications:

• 32-bit ARM Cortex-M3 processor 72 MHz
• 64 kB flash memory, 20 kB SRAM
• USB and CAN controllers
• 32 kHz crystal for RTC
• dual 1 us A/D converter, DMA controller
• SPI, UART, I2C
• Serial wire debug (SWD) & JTAG interfaces

• 7 timers

You might also see this ARM Cortex M3 STM32F103C8T6 board advertised as an ‘Arduino’ board. Although it is not really an Arduino, the guys at stm32duino.com have developed a means to integrate it into the Arduino IDE. They have also ported some of the Arudino libraries to support this board. However, do not expect every library supported for an Arduino to work on this processor. For more information on what works and what might not, check out the stm32duino forum HERE.

This board is easily programmed with a ‘standard’ USB to Serial converter from FTDI or SILABS or an ST-LINK V2 in-circuit debugger and programmer from STMicroelectronics. These devices communicate with the bootloader which is stored in the internal boot ROM memory (system memory) of STM32 devices. This bootloader is programmed by STMicroelectronics during production and its main purpose is to download the application program to internal FLASH memory.

My preference is the ST-LINK V2 since it also functions as an in-circuit debugger. OPENOCD.org fully supports the ST-LINK V2 and the STM32F103C8T6 board. OCD (On Chip Debugging) comes in quite handy to diagnose those ‘complexities’ 😎 in your code.

To program it, you might need to change the BOOT0 and/or BOOT1 jumpers as those pins select how the STM32F103C8T6 starts.

Here is what the STM32F103C8T6 looks like attached to an ST-LINK V2 programmer and a SILABS CP2102 USB – Serial converter: