The STM32F4DISCOVERY helps you to discover the STM32F407/417 line features and to develop your applications easily. It includes everything required for beginners and experienced users to get started quickly. Key Features: STM32F407VGT6 microcontroller featuring 32-bit ARM Cortex-M4F core, 1 MB Flash, 192 KB RAM in an LQFP100 package. On-board ST-LINK/V2 with selection mode switch to use the kit as a standalone ST-LINK/V2 (with SWD connector for programming and debugging). Board power supply: through USB bus or from an external 5 V supply voltage. External application power supply: 3 V and 5 V. LIS302DL or LIS3DSH ST MEMS 3-axis accelerometer. MP45DT02, ST MEMS audio sensor, omni-directional digital microphone. CS43L22, audio DAC with integrated class D speaker driver. Eight LEDs. Two push buttons (user and reset). USB OTG FS with micro-AB connector.

High-Performance Applications Processing for Mobile and Enterprise Markets

The ARM Cortex-A series of applications processors provide a range of solutions for devices undertaking complex compute tasks, such as hosting a rich Operating System (OS) platform, and supporting multiple software applications. Cortex-A series processors scale efficiently across a range of the highest performing consumer, embedded and enterprise devices. These include a spectrum of smartphones, mobile computing platforms, digital TVs, set-top boxes, and rich IoT devices through to enterprise networking, and server solutions. In an increasingly energy-conscious business landscape, the power efficiency of Cortex-A processors can provide significant advantages.

Ultimate Reliability for Embedded Real-Time Processing

The ARM Cortex-R real-time processors offer high-performance computing solutions for embedded systems where reliability, high availability, fault tolerance, maintainability and deterministic real-time responses are essential. The Cortex-R series processors provide fast time-to-market through proven technology shipped in billions of products, and leverages the vast ARM ecosystem and global, local language, 24/7 support services to ensure rapid and low-risk development. Cortex-R series processors deliver fast and deterministic processing and high performance, while meeting challenging real-time constraints in a range of situations. They combine these features in a performance, power and area optimized package, making them the trusted choice in reliable systems demanding high error-resistance.

Scalable and Low-Power Technology for any Embedded Market

The ARM Cortex-M processor family is a range of scalable and compatible, energy efficient, easy to use processors designed to help developers meet the needs of tomorrows smart and connected embedded applications. Those demands include delivering more features at a lower cost, increasing connectivity, better code reuse and improved energy efficiency. The Cortex-M family is optimized for cost and power sensitive MCU and mixed-signal devices for applications such as Internet of Things, connectivity, smart metering, human interface devices, automotive and industrial control systems, domestic household appliances, consumer products and medical instrumentation.

USART stands for Universal Synchronous Asynchronous Receiver Transmitter. It is sometimes called the Serial Communications Interface or SCI. Synchronous operation uses a clock and data line while there is no separate clock accompanying the data for Asynchronous transmission. Since there is no clock signal in asynchronous operation, one pin can be used for transmission and another pin can be used for reception. Both transmission and reception can occur at the same time. This is known as full duplex operation. The universal asynchronous receiver/transmitter (UART) takes bytes of data and transmits the individual bits in a sequential fashion. At the destination, a second UART re-assembles the bits into complete bytes. Serial transmission of digital information (bits) through a single wire or other medium is less costly than parallel transmission through multiple wires.

Serial to Peripheral Interface (SPI) is a hardware/firmware communications protocol developed by Motorola and later adopted by others in the industry. Microwire of National Semiconductor is same as SPI. Sometimes SPI is also called a “four wire” serial bus. The Serial Peripheral Interface or SPI-bus is a simple 4-wire serial communications interface used by many microprocessor/microcontroller peripheral chips that enables the controllers and peripheral devices to communicate each other. Even though it is developed primarily for the communication between host processor and peripherals, a connection of two processors via SPI is just as well possible. The SPI bus, which operates at full duplex (means, signals carrying data can go in both directions simultaneously), is a synchronous type data link setup with a Master / Slave interface and can support up to 1 megabaud or 10Mbps of speed.

I2C was originally developed in 1982 by Philips for various Philips chips. It is used for attaching lower-speed peripherals to processors on computer motherboards and embedded systems. Each I2C bus consists of two signals: SCL and SDA. SCL is the clock signal, and SDA is the data signal. The clock signal is always generated by the current bus master; some slave devices may force the clock low at times to delay the master sending more data (or to require more time to prepare data before the master attempts to clock it out). Unlike UART or SPI connections, the I2C bus drivers are open drain, meaning that they can pull the corresponding signal line low, but cannot drive it high. Thus, there can be no bus contention where one device is trying to drive the line high while another tries to pull it low, eliminating the potential for damage to the drivers or excessive power dissipation in the system.

In many microcontroller projects you need to read and write data. It can be reading data from peripheral unit like ADC and writing values to RAM. In other case maybe you need send chunks of data using SPI. Again you need to read it from RAM and constantly write to SPI data register and so on. When you do this using processor,  you loose a significant amount of processing time. In order to avoid occupying CPU most advanced microcontrollers have DMA unit. As its name says DMA does data transfers between memory locations without need of CPU. Low and medium density ST32 microcontrollers have single 7 channel DMA unit while high density devices have two DMA controllers with 12 independent channels. In STM32VLDiscovery there ST32F100RB microcontroller with single DMA unit having 7 channels. DMA can do automated memory to memory data transfers, also do peripheral to memory and peripheral to peripheral.

Microcontrollers are capable of detecting binary signals: is the button pressed or not? These are digital signals. When a microcontroller is powered from five volts, it understands zero volts (0V) as a binary 0 and a five volts (5V) as a binary 1. The world however is not so simple and likes to use shades of gray. What if the signal is 2.72V? Is that a zero or a one? We often need to measure signals that vary; these are called analog signals. A 5V analog sensor may output 0.01V or 4.99V or anything inbetween. Luckily, nearly all microcontrollers have a device  called ADC built into them that allows us to convert these voltages into values that we can use in a program to make a decision. An Analog to Digital Converter (ADC) is a very useful feature that converts an analog voltage on a pin to a digital number.

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