STM32

The STM32 family is developed and manufactured by STMicroelectronics. They are considered advanced and efficient and are known for great technical documentation, versatility, performance, energy efficiency, and reliability. They are also highly configurable and provide a wide range of features.
For a long time, STM32 delivered MCUs without radio modules; thus, they required external radio communication interfaces for IoT applications. Recently, a series of chips have been available with built-in radio modules, primarily using IEEE 802.15.4 (Zigbee, Thread, and other wireless sensor network protocols) rather than 802.11 (WiFi).

STM manufacturer provides developers with development kits, some of which can accommodate popular Arduino shields. They also offer a development SDK based on the popular Eclipse platform (implemented with Java, thus cross-platform). They also ensure at least 10 years of availability and support.

STM32 MCUs are known for their energy-efficient operation, making them suitable for battery-powered and low-power IoT applications.

Thanks to the built-in performance options such as an independent vectorised interrupt system and DMA, industrial grade series can handle video processing, TFT displays, and so on.

STM32 SoCs use ARM Cortex-based cores, starting from M0 to M7 ^[1]. Some of the SoCs integrate 2 cores, such as in the case of the radio-equipped models, where the main core is supported by the extra one (usually M0+), which handles wireless communication protocols. All MCUs are 32-bit. Some STM32 MCUs tend to tolerate a broader range of powering voltages. Thus, they may operate on raw battery cells without needing a voltage conversion and stabilisation.

There are 5 major series of the microcontrollers and microprocessors manufactured by STM:

• High-performance series with Cortex M3 up to Cortex M7.
• Mainstream series with Cortex M0 to Cortex M7.
• Ultra-low power series with Cortex M0+, via Cortex M4, up to Cortex M33.
• Wireless series, with Cortex M4, Cortex M33 and radio coprocessor Cortex M0+.
• Industrial grade MP1 microprocessor series, with a mixture of Cortex A7 and Cortex M4 cores (some chips use only A7 core).

All STM32 use ARM Cortex cores, single, double or in pair with another ARM core coprocessor, such as in the case of the industrial grade (MP1) microprocessors and wireless (STM32W) microcontrollers series.

Maximum frequencies depend on the ARM Core model and are between 32MHz for Cortex M0+ cores and 550MHz for H7. Industrial series MP1 hits even 1GHz.

Built-in RAM, flash, and EEPROM sizes depend on the family of chips and the exact model within this family. Ultra-low-power devices such as STM32L0 microcontroller have only 2kB of RAM, 128B of EEPROM, and 16kB of flash. Conversely, the STM32H7 microcontroller can have up to 1184kB of RAM and 2MB of built-in flash. Most MCUs can extend the memory externally with SPI (even up to dual QSPI interface). Each STM32 series has its variations that vary in the built-in memory size.

Only the STM32 W series provides radio connectivity integrated into the MCU. Currently, there are 4 chip series (and each has its variations regarding enclosure size, memory size (both RAM and flash), number of GPIO pins available, and some advanced functions such as secure keys management, secure boot, etc.:

• STM32 WL series ^[2] introducing LoRaWAN, Sigfox, W-MBUS, mioty, and virtually other protocols compatible with (G)FSK, (G)MSK, and BPSK modulations in a single chip,
• STM32 WB0 series ^[3] designed for energy-efficient applications and Bluetooth 5.3 only,
• STM32 WB series ^[4] with Zigbee, Thread (OpenThread), Matter and Bluetooth 5.4 and BLE, Zephyr and Cordio stacks,
• STM32 WBA series ^[5] with Bluetooth 5.3.

Each series has variations, e.g., the STM32 WL series has STM32WLE5 and STM32WL54 that do not support LoRa, as well as versions STM32WLE5 and STM32WL55 with LoRa.

The STM32 family provides all peripherals and interfaces, but availability and amount depend on the family, series, and particular model. STM32 MCUs connect the CPU core to various peripheral modules using a peripheral bus matrix. This matrix allows for flexible routing of communication between the CPU and peripherals. Each peripheral block has associated control registers allowing configuring and controlling their operation. Those registers can be used to set parameters, turn features on or off, and monitor the status of the peripherals.

Peripherals include:

• GPIO,
• timers (including hardware-based pulse generation such as PWM and watchdog timers),
• embedded system protocol interfaces UART (USART), SPI (even up to dual QSPI), I2C, CAN,
• ADC and DAC converters,
• USB, Ethernet, SDIO, camera (CSI), display (DSI),
• RTC interface,
• DMA,
• interrupt controller,
• security and cryptography functions modules.

STM32 has efficient and highly configurable clocks, an NVIC interrupt controller (Nested Vectored Interrupt Controller), and a DMA that, along with timers, provide great capabilities for Real-Time applications of high performance and reliability. Figure 1 presents a sample STM32G4 configuration for clocks.

Some STM32 MCUs provide computing performance high enough to handle image and video processing, e.g. STM32F7 and STM32H7 series have hardware-accelerated jpeg (and thus mjpeg) encoding and decoding. MP1 series can be equipped with an optional GPU for 3D acceleration. Some of the MCUs include a built-in TFT display controller.

STM32 shares a common ARM architecture but, depending on the family, has different cores and, thus, performance and applications. The following chapters show a more in-depth review of the STM32 MCU hardware.

STM provides developers with popular development boards virtually for any family of MCUs. There are also available 3rd party development boards.

There are three types of development boards available (obviously, not for all series):

• Nucleo series that share pinout with Arduino, enabling an easy use of Arduino shields. They provide developers with a built-in ST-link hardware debugger.
• Discovery kits, bigger in size and usually rich in connectors, frequently equipped with external sensors such as MEMS (gyro, accelerometer), microphone, LEDs and so on. They provide developers with a built-in ST-link hardware debugger.
• Evaluation boards are a more advanced version of the Discovery Kits, equipped with a display, external memory, etc. Their purpose is to demonstrate all capabilities of the particular MCU.

Sample USB stick, Nucleo kit and development kit for STM32WB55 are present in figures: 2, 3 and 4, respectively.

Sample 3rd party evaluation board for STM32F1 MCU is present in the figure 5.