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1 Overview of STM32 Basic Knowledge#

1.1 Introduction to STM32#

STM32 is a 32-bit microcontroller developed by STMicroelectronics based on the ARM Cortex-M core.

M stands for Microcontroller.

STM32 is commonly used in embedded fields such as smart vehicles, drones, robots, wireless communication, the Internet of Things, industrial control, and entertainment electronic products.

STM32 is powerful, has excellent performance, rich on-chip resources, and low power consumption, making it a classic embedded microcontroller.

1.2 Introduction to ARM#

ARM refers to both ARM Holdings and ARM processor cores.

ARM Holdings is a leading global semiconductor intellectual property (IP) provider, with over 95% of smartphones and tablets worldwide using ARM architecture.

ARM Holdings designs ARM cores, while semiconductor manufacturers enhance the core's peripheral circuits and produce chips.

1.3 Introduction to STM32F103C8T6#

Series: Mainstream series STM32F1

Core: ARM Cortex-M3

Main frequency: 72MHz

RAM: 20K (SRAM)

ROM: 64K (Flash)

Power supply: 2.0~3.6V (Standard 3.3V)

Package: LQFP48

1.4 On-chip Resources/Peripherals#

STM32 can integrate operating systems such as FreeRTOS, UCOS, etc. If these operating systems are used, SysTick is required to provide timing for task switching.

UART stands for asynchronous serial port, while STM32's USART supports both asynchronous and synchronous serial ports, with asynchronous serial ports being more commonly used.

1.5 Chip Naming Convention#

1.6 System Architecture#

The Cortex-M3 core features three buses: ICode instruction bus, DCode data bus, and System bus.

The ICode and DCode buses are primarily used to connect to Flash memory.

Flash stores the programs we write.

The ICode instruction bus is used to load program instructions.

The DCode data bus is used to load data, such as constants and debug data.

The System bus connects to SRAM and FSMC.

SRAM is used to store variable data during program execution.

The AHB system bus is used to mount major peripherals; AHB stands for Advanced High-performance Bus, typically mounting the most basic or high-performance peripherals, such as reset and clock control circuits. SDIO is also mounted on AHB.

APB1 and APB2 are two peripheral buses; APB stands for Advanced Peripheral Bus, used to connect general peripherals.

Due to differences in bus protocols, speeds, and data transfer formats between AHB and APB, two bridges are needed to complete data conversion and buffering. The overall performance of AHB is higher than that of APB, with APB2 generally having higher performance than APB1. APB2 typically operates at the same frequency as AHB, which is 72MHz, while APB1 generally operates at 36MHz. Therefore, APB2 usually connects to slightly more important peripherals, such as GPIO ports and some key peripherals (USART1, SPI1, TIM1, TIM8, etc.). TIM8, like TIM1, is also a high-end timer, making it an important peripheral. ADC, EXTI, and AFIO are also connected to APB2. Other peripherals like 2, 3, 4, 5, DAC, PWR, and BKP, which are less critical, are allocated to APB1. However, in practice, users generally do not notice performance differences between APB2 and APB1; it is sufficient to know which bus a peripheral is mounted on.

DMA can be seen as a small secretary for the CPU, handling tasks like moving large amounts of data, which would waste CPU time. DMA primarily handles these simple and repetitive tasks. It connects to the bus matrix via the DMA bus and has the same bus control rights as the CPU to access these peripherals. When DMA is needed to transfer data, the peripheral sends a DMA request via the request line, and DMA gains bus control to access and transfer data, all without CPU involvement, saving CPU time for other tasks.

1.7 Pin Definitions#

The red pins are related to power supply.

The blue pins are related to the minimum system.

The green pins are I/O ports and functional pins.

S type represents power supply.

I type represents input.

O type represents output.

IO type represents input/output.

FT indicates that this pin can tolerate 5V voltage; those without FT can only tolerate 3.3V voltage.

STM32 uses a partitioned power supply method, with multiple power supply pins. When using, VSS is connected to GND, and VDD is connected to 3.3V.

STM32 supports two debugging methods: SWD and JTAG.

SWD requires two lines, SWDIO and SWCLK.

JTAG requires five lines: JTMS, JTCK, JTDI, JTDO, NJTRST.

STLINK uses the SWD method to download and debug programs, so it only occupies PA13 and PA14 I/O ports.

When downloading using SWD, PA15, PB3, and PB4 can be switched to ordinary I/O ports, but this needs to be configured in the program; by default, they will not be used as I/O ports.

1.8 Boot Configuration#

The purpose of the boot configuration is to specify where the program starts running. Generally, programs execute from the Flash program memory, but in certain cases, we can also start the program from other locations to achieve special functions.

BOOT1=0 BOOT0=1 mode is used for serial port downloading; the system memory stores a segment of the BootLoader program in STM32. The role of the BootLoader program is to receive data from the serial port and refresh it to the main flash memory, allowing programs to be downloaded via the serial port. Typically, we configure this mode when we need to download programs via the serial port.

BOOT0=0 sets the boot mode to the main flash memory mode, where the main flash memory is selected as the startup area, and the program inside the flash memory is executed normally. This mode is the most commonly used mode and is generally the default configuration.

BOOT1=1 BOOT0=1 configures for SRAM startup, which is mainly used for program debugging and is currently used less frequently.

The value of the BOOT pin is valid at the moment of power-up reset; afterwards, it can be arbitrary.

1.9 Minimum System Circuit#

OSC32 refers to a 32.768KHz crystal oscillator; 32768 is 2 raised to the power of 15, and the internal RTC circuit can generate a 1-second time signal through a division of 2 raised to the power of 15.

RTC crystal oscillator is a 32.768KHz crystal.