STM32 Microcontroller USB Communication Complete Guide: Detailed Explanation of USB Protocols, Configuration, and Applications, Connecting to the World

# The Complete Guide to STM32 MCU USB Communication: Exploring the USB Protocol, Configuration, and Applications to Connect with the World

# 1. Fundamentals of USB Communication

USB (Universal Serial Bus) is a widely used standard protocol for communication between computers and peripheral devices. It is renowned for its high speed, cost-effectiveness, and ease of use. This chapter will introduce the basic knowledge of USB communication, including the physical layer, data transmission methods, protocol stack, and communication process.

# 2. In-depth Explanation of the USB Protocol

### 2.1 USB Physical Layer and Data Transmission

The USB physical layer defines the physical connection and data transmission method between USB devices. It includes:

- **Connectors:** There are various types of USB connectors, including Type-A, Type-B, and Type-C. They provide physical connections and power.
- **Wiring:** USB cables typically contain four wires: power (VBUS), ground (GND), data+ (D+), and data- (D-).
- **Signals:** USB data transmission uses differential signaling, where the voltage difference between the D+ and D- lines represents data.

Data transfer rates depend on the USB version:

| USB Version | Speed |
|---|---|
| USB 1.0 | 1.5 Mbps |
| USB 1.1 | 12 Mbps |
| USB 2.0 | 480 Mbps |
| USB 3.0 | 5 Gbps |
| USB 3.1 | 10 Gbps |

### 2.2 USB Protocol Stack and Communication Process

The USB protocol stack is a layered architecture that defines how data is transmitted between USB devices. It includes:

- **Physical Layer:** Defines physical connections and data transmission.
- **Data Link Layer:** Processes data frames and error detection.
- **Transport Layer:** Manages data transmission and flow control.
- **Application Layer:** Provides an interface with applications.

The USB communication process involves the following steps:

1. **Device Enumeration:** The host detects and recognizes the connected USB device.
2. **Address Assignment:** The host assigns a unique address to the device.
3. **Configuration:** The host and device negotiate the device's configuration and capabilities.
4. **Data Transmission:** The host and device exchange data.
5. **Disconnection:** The device or host disconnects.

**Code Block:**

// Example of USB device enumeration
USB_Init();
USB_Connect();
while (USB_IsConnected()) {
     // Process data transmission
}
USB_Disconnect();

**Logical Analysis:**

This code demonstrates the USB device enumeration process. It initializes the USB peripheral, connects to the host, and processes data transmission while the device is connected.

**Parameter Explanation:**

- `USB_Init()`: Initializes the USB peripheral.
- `USB_Connect()`: Connects to the USB host.
- `USB_IsConnected()`: Checks if the USB device is connected.
- `USB_Disconnect()`: Disconnects from the USB host.

# 3.1 USB Peripheral Configuration and Registers

STM32 microcontrollers integrate USB peripherals, which enable USB communication functionality by configuring their registers. The main registers involved include:

- **USB_OTG_FS/HS_DCFG**: USB device configuration register, used to configure device speed, mode, and clock source.
- **USB_OTG_FS/HS_DCTL**: USB device control register, used to control the connection and disconnection of USB devices.
- **USB_OTG_FS/HS_DIEPMSK**: USB device endpoint transmit interrupt mask register, used to mask endpoint transmit interrupts.
- **USB_OTG_FS/HS_DOEPMSK**: USB device endpoint receive interrupt mask register, used to mask endpoint receive interrupts.
- **USB_OTG_FS/HS_DIEPCTLx**: USB device endpoint transmit control register, used to control the transmit mode, packet size, and transmit type of endpoints.
- **USB_OTG_FS/HS_DOEPCTLx**: USB device endpoint receive control register, used to co