The STM32F407 is a high-performance microcontroller from STMicroelectronics based on the ARM Cortex-M4 core. It offers advanced features making it suitable for a wide range of embedded applications requiring high performance and low power consumption.
Key Features
- ARM Cortex-M4 Core – The STM32F407 is based on ARM’s Cortex-M4 core which includes a floating point unit (FPU) and achieves 225 DMIPS/606 CoreMark executing from Flash memory at up to 168 MHz clock frequency.
- Memory – The STM32F407 has up to 1 MB of flash memory for storing code and data. It also has up to 192 KB of SRAM for data and the call stack. The flash and SRAM are on separate bus matrices for higher performance.
- Clock Speed – The maximum clock frequency is 168 MHz. The microcontroller has internal oscillators as well as external clock inputs.
- Timers – There are 14 general purpose timers including advanced motor control, basic, general-purpose, advanced-control, and basic timers. Some timers can be combined to create a higher-resolution timer.
- Communication Interfaces – The STM32F407 supports various communication protocols including CAN, I2C, SPI, UART/USART, SDIO, USB, Ethernet, etc. There are up to 3 I2C interfaces, 6 USARTs, 3 SPI interfaces, 2 CAN interfaces, and more.
- Analog Inputs – It has up to 21 analog inputs that can be individually configured as single-ended or differential channels. The resolution is 12-bit.
- Advanced Peripherals – Some advanced peripherals include a Cryptographic processor for AES encryption/decryption, a hash processor, and a True Random Number Generator.
- Low Power – The microcontroller provides various power saving modes including sleep, stop, and standby. Dynamic voltage scaling allows real-time adjustment of speed versus power consumption.
- Debugging – Debugging is supported through SWD and JTAG interfaces. The STM32F407 is compatible with the ST-LINK/V2 debugger.
- Packages – The microcontroller comes in various packages with up to 144 pins and is pin-to-pin compatible across many STM32 families for easy migration.
ARM Cortex-M4 Core
The heart of the STM32F407 is ARM’s 32-bit Cortex-M4 core running at frequencies up to 168 MHz. The Cortex-M4 architecture includes an FPU that supports single-precision and double-precision arithmetic for faster complex math operations. DSP instructions are also supported by the core. The Cortex-M4 achieves 225 DMIPS and 606 CoreMark at 168 MHz while executing code from Flash memory.
The Cortex-M4 is a very popular core used across various microcontroller families from STMicroelectronics, NXP, Microchip, and other vendors. It provides an optimal balance of performance and power efficiency for embedded applications. The combination of high speed, FPU, DSP extensions, and low power consumption makes the Cortex-M4 well suited for applications in automation, robotics, industrial, IoT, etc.
Memory Resources
The STM32F407 comes with flexible memory options to suit different application requirements.
Flash Memory
There is up to 1 MB of flash memory for storing firmware code and data. Flash memory allows the microcontroller firmware and data to persist even when power is removed. The STM32F407 flash memory interface includes error correction code (ECC), read-while-write capability, and flash cache to accelerate execution speed.
SRAM
For data storage and the stack, the STM32F407 includes 128 KB to 192 KB of static RAM. This provides fast access for time-critical operations during code execution compared to flash memory. There are separate bus matrices for connecting the Cortex-M4 core to flash memory and SRAM to enable concurrent access and higher performance.
External Memory
The memory controller supports adding more external memories through various interfaces like the FSMC parallel interface, SRAM interface, Quad SPI interface for external flash, etc. This allows expanding the memory capabilities for data logging, multimedia processing, or other memory-intensive tasks.
Clock Speed and Oscillators
The maximum clock frequency of the STM32F407 is 168 MHz. However, it can be configured to run at lower speeds for reduced power consumption. The core clock is derived from internal or external oscillators.
For internal oscillators, there is a 16 MHz high-speed internal (HSI) RC oscillator as well as 32 kHz, 40 kHz, and 48 MHz options. The 16MHz HSI RC oscillator is commonly used to generate the system clock. There are also internal PLLs that can scale the internal oscillator speeds for higher core/peripheral clocks.
Alternatively, a more accurate external crystal oscillator can be connected to the microcontroller’s external oscillator (Xtal) pins. Common crystal frequencies are 8 MHz or 25 MHz. The external oscillator can similarly be scaled by internal PLLs.
Having both internal and external oscillator options allows optimizing the STM32F407 for applications requiring either low-cost system clock generation or highly accurate timing. The clock speeds can also be adjusted dynamically at runtime for performance versus power consumption tradeoffs.
Timers
Timers are important peripherals in microcontrollers for generating precise delays, PWM signals, triggering interrupts at fixed intervals, and other real-time control applications. The STM32F407 includes a comprehensive set of advanced timers.
In total there are 14 general-purpose timers that are based on a 16-bit or 32-bit counter running on either the APB1 or APB2 clock. Each timer has individual clock prescalers, up to 4 capture/compare channels, and other capabilities.
The timer types include:
- 2 x 32-bit timers with up to 4 IC/OC/PWM channels per timer
- 2 x 16-bit advanced motor control timers stepping the main output
- 2 x 16-bit general-purpose timers with OC/PWM and IC/Input Capture
- 2 x 16-bit basic timers
- 1 x SysTick timer
- 2 x watchdogs
- 1 x SysTick timer
This flexible assortment of timers allows serving various time-critical functions in embedded applications. The timers can also be cascaded to create higher resolution timers using multiple timer channels.
Communication Interfaces
The STM32F407 includes a wide selection of serial and parallel communication peripherals for interfacing with external devices. This allows it to serve as a communications bridge in an embedded system.
Serial Interfaces
- 3 x I2C – Up to 3 I2C modules support the standardized I2C serial protocol running at up to 400 kHz (Fast mode) or 1 MHz (Fast Plus mode). Each I2C interface can be configured as either master or slave.
- 6 x USARTs – Up to 6 Universal Synchronous/Asynchronous Receiver/Transmitters provide async or sync serial. Features include RS-232, RS-485, IrDA, LIN, Smartcard mode, and multprocessor communications in master/slave mode. The top USART speed is 10.5 Mbit/s.
- 3 x SPI – The Serial Peripheral Interfaces (SPIs) allow communicating with external peripherals in full duplex mode. Speeds up to 42 Mbit/s are supported.
- 2 x CAN – Dual CAN controllers support the CAN 2.0A and CAN 2.0B protocols for industrial automation networks and automotive applications.
- SPDIFRX interface – Sony/Philips Digital Interface Format Receiver provides input support for digital audio streams.
Parallel Interfaces
- Camera interface – Provides interfacing capabilities for CMOS camera sensors and CCDs.
- FSMC interface – The Flexible Static Memory Controller supports interfacing to external memories including SRAM, PSRAM, NOR and NAND memories.
- Quad SPI interface – Supports attaching external flash memory using the Serial Peripheral Interface.
Covering such a wide variety of serial and parallel interfaces allows the STM32F407 to connect with most types of external peripherals and devices encountered in embedded applications.
Analog Inputs
The STM32F407 includes a flexible analog interface with up to 21 analog input channels. This allows sampling various analog sensors and input signals.
Key analog features:
- Up to 21 analog input channels
- 12-bit successive approximation ADC
- 2.4 MSPS ADC conversion rate
- Single or differential input mode
- Configurable sample times
- Scan conversion mode
- DMA for transferring samples to memory without CPU intervention
- Analog watchdog
- Temperature sensor
The successive approximation ADC supports fast 12-bit analog readings. The inputs can be individually configured for single-ended or differential connections. Multiple channels can be grouped into a scan group that converts across each channel in a back-to-back sequence.
An analog watchdog is available to monitor input channels and trigger an alert if readings go outside allowable high/low thresholds. A temperature sensor enables measuring the internal microcontroller temperature.
Overall, the analog subsystem provides a rich set of capabilities for interfacing the microcontroller to various analog sensors and systems.
Advanced Peripherals
In addition to the standard embedded peripherals, the STM32F407 includes several advanced peripheral units for unique applications.
Cryptographic Processor
A cryptographic coprocessor provides hardware acceleration for AES encryption/decryption up to 256-bit keys and hash algorithms like MD5 and SHA-1. This enables secure communication capabilities.
Random Number Generator
The True Random Number Generator collects entropy from various noise sources within the microcontroller and processes it to generate true random numbers. This provides a source of randomness for applications like encryption keys.
LCD Interface
The LCD parallel interface allows driving graphical LCD displays. The resolution can range from 1-bit monochrome up to 16-bit color depending on the display device.
Low Power Operation
The STM32F407 implements various power-saving measures to minimize current draw in embedded applications where low power consumption is critical.
Idle power is reduced through clock gating of unused peripherals and the Cortex-M4 core entering sleep mode when idle. Further savings come from dynamically scaling the CPU speed using the internal PLLs and flash memory wait states.
For lowest power stop and standby modes are available. Stop mode disables the main PLL and HSI RC oscillator. Standby mode goes further by powering down SRAM and peripherals while keeping wake-up sources active. Wake-up can occur from external interrupts, the internal watchdog timer, RTC alarm, tamper detector, and other sources.
With careful use of power modes and dynamic voltage scaling, the STM32F407 power consumption can be minimized to extend battery life in portable electronics.
Debugging Capability
The STM32F407 supports debugging through both the SWD (Serial Wire Debug) and JTAG interfaces. This allows for setting breakpoints, accessing registers, downloading code, and other debugging tasks.
The commonly used debugging tool is STMicro’s ST-LINK/V2 which communicates through the SWD interface. It provides a virtual COM port for log tracing and integrates with various IDEs like STM32CubeIDE, Keil MDK-ARM, and IAR Workbench.
Debugging and downloading code is simplified through the integrated bootloader supporting UART, CAN, USB, Ethernet, etc. for flashing firmware.
Packages
The STM32F407 is available in a range of surface mount packages from 64 pins up to 144 pins. Quad flat packages (QFP) as well as BGA packages are available. Across STM32 families the pinouts are compatible, easing migration between microcontrollers.
Some example packages include:
- LQFP64 – 64-pin plastic LQFP package, 10×10 mm
- LQFP100 – 100-pin plastic LQFP package, 14×14 mm
- LQFP144 – 144-pin plastic LQFP package, 20×20 mm
- UFBGA176 – 176-pin plastic BGA, 10×10 mm
The wide range of packaging options allows optimizing PCB footprint size from smaller 64-pin designs up to high I/O count BGA designs.
Conclusion
The STM32F407 integrates ARM’s powerful Cortex-M4 core with advanced peripherals and low power operation. For embedded systems that require floating point capability, high performance, digital signal processing, and extensive peripheral connectivity, the STM32F407 is an excellent choice.
With capabilities like the FPU, efficient 16 MHz system clock generation, flexible timers, advanced communication interfaces, broad I/O configuration, and various power saving modes, the STM32F407 can fulfill the key requirements of embedded control, monitoring, and processing applications across many industries.
