Essential Knowledge for Embedded Development! In-Depth Analysis and Practical Guide to 10 Core Interface Protocols

Table of Contents

• Introduction: Interface Protocols – The “Digital Language” of Embedded Systems
• 1. Low-Speed Communication Interfaces: Efficient Solutions for Simple Scenarios
• 2. High-Speed Communication Interfaces: The Backbone of Large Data Transmission
• 3. Specialized Domain Interfaces: “Specialists” for Specific Scenarios
• 4. Practical Applications and Selection Guide for Interface Protocols
• 5. Interactive Poll: Which Embedded Interface Do You Use Most Often?
• 6. Summary and Recommended Advanced Resources

Introduction: Interface Protocols – The “Digital Language” of Embedded Systems

In the field of embedded development, data exchange between devices relies on various interfaces and protocols, which serve as the “digital language” for communication between different devices. From the transmission of sensor data in smart wristbands to the collaborative control of ECUs in autonomous vehicles, mastering these “languages” is a fundamental requirement for every embedded engineer. This article will deeply analyze 10 core interface protocols, combining practical code, timing diagrams, and selection guides to help you quickly become an expert in embedded development!

1. Low-Speed Communication Interfaces: Efficient Solutions for Simple Scenarios

1. UART: The Classic Asynchronous Communication Interface

UART (Universal Asynchronous Receiver-Transmitter) is the most basic communication interface in embedded development, using asynchronous serial communication without the need for an additional clock line. It achieves full-duplex communication through a transmit line (TX) and a receive line (RX). The two communicating parties synchronize data by agreeing on a baud rate (e.g., 9600bps, 115200bps), and data is transmitted in frames that include a start bit, data bits, a parity bit, and a stop bit.

Usage Scenarios: Commonly used for debugging communication between microcontrollers and PCs (e.g., via USB-TTL modules) and for sensor data acquisition (e.g., temperature and humidity sensors).Bandwidth: Typically ranges from 1200bps to 460.8kbps, with a maximum of several Mbps.Disadvantages: No hardware flow control mechanism; mismatched baud rates can lead to data loss; limited transmission distance (approximately 15 meters for RS232).

Code Example (Arduino):

void setup() {
  Serial.begin(9600); // Initialize UART with baud rate 9600
}

void loop() {
  if (Serial.available() > 0) { // Check if data is available
    char data = Serial.read(); // Read data
    Serial.print("Received: ");
    Serial.println(data);
  }
}

2. I2C: A Minimal Two-Wire Multi-Device Communication Protocol

I2C (Inter-Integrated Circuit) requires only two wires (clock line SCL and data line SDA) to achieve multi-device communication, using a synchronous half-duplex mode. Each device is distinguished by a 7-bit or 10-bit address and supports a multi-master arbitration mechanism to avoid communication conflicts.

Usage Scenarios: Commonly used to connect EEPROMs, temperature and humidity sensors, real-time clock modules, and other low-speed devices.Bandwidth: Standard mode 100kbps, fast mode 400kbps, high-speed mode 3.4Mbps.Disadvantages: Limited bus load capacity (approximately 10 devices); long-distance communication is prone to interference.

Code Example (Python, based on smbus library):

import smbus

bus = smbus.SMBus(1) # Create I2C object, 1 indicates I2C bus number
address = 0x48 # Device address

# Read device data
data = bus.read_i2c_block_data(address, 0, 2)
print(f"Received data: {data}")

3. SPI: The “Speed Champion” of High-Speed Serial Communication

SPI (Serial Peripheral Interface) is a high-speed synchronous serial communication protocol that uses full-duplex mode. It communicates between the host and slave devices through a clock line (SCK), master out slave in line (MOSI), master in slave out line (MISO), and chip select line (CS). The host selects the slave device using the CS signal and provides clock synchronization for data transmission.

Usage Scenarios: Suitable for high-speed data transmission scenarios, such as communication between MCUs and Flash, ADCs, gyroscopes, etc.Bandwidth: Can reach several tens of Mbps, depending on the clock frequency.Disadvantages: Requires multiple signal lines, not suitable for complex networks with multiple slaves; lacks an acknowledgment mechanism, requiring software error handling.

Timing Diagram:

sequenceDiagram
    participant Host as Host
    participant Slave as Slave
    Host-->>Slave: CS pulled low, select slave
    Host-->>Slave: Send SCK clock signal
    loop Data Transmission
        Host-->>Slave: Send data via MOSI
        Slave-->>Host: Return data via MISO
    end
    Host-->>Slave: CS pulled high, deselect

2. High-Speed Communication Interfaces: The Backbone of Large Data Transmission

1. USB: The “Universal Key” for Peripheral Connections

USB (Universal Serial Bus) is the most widely used interface standard, supporting hot-swapping and plug-and-play, with a host-controlled architecture. From USB 1.1 (12Mbps) to USB 4 (40Gbps), it continuously breaks through transmission speed limits.

Usage Scenarios: Connecting various peripherals (USB drives, keyboards, cameras), device charging, and data transmission.Disadvantages: Complex protocol requiring dedicated controllers; high cable requirements for high-speed transmission.

2. Ethernet: The Cornerstone of Network Communication

Ethernet is based on the TCP/IP protocol stack and achieves high-speed network communication through RJ45 interfaces, supporting various rates such as 10M/100M/1G/10G. In full-duplex mode, it allows for collision-free data transmission.

Usage Scenarios: Computer networking, industrial automation, smart home gateways.Code Example (ESP32, Arduino Framework):

#include <wifi.h>
#include <wificlient.h>

const char* ssid = "your_SSID";
const char* password = "your_PASSWORD";

void setup() {
  Serial.begin(115200);
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(1000);
    Serial.println("Connecting to WiFi...");
  }
  Serial.println("Connected to WiFi");
}

void loop() {
// Network communication logic
}
</wificlient.h></wifi.h>

3. MIPI: The Exclusive High-Speed Channel for Mobile Devices

MIPI (Mobile Industry Processor Interface) is designed specifically for mobile devices, such as smartphone cameras (CSI-2) and displays (DSI), using low-voltage differential signaling, with a single lane supporting up to 2.5Gbps and supporting multi-lane parallel transmission.

Usage Scenarios: Internal high-speed data transmission in smartphones and tablets.Disadvantages: Complex protocol, high development threshold, poor compatibility.

4. EDP: The Unsung Hero of High-Definition Displays

EDP (Embedded DisplayPort) is based on the DisplayPort protocol and is used for connecting displays in laptops and embedded devices, supporting 4K/8K video transmission.

Usage Scenarios: High-definition video transmission between displays and GPUs/SoCs.Bandwidth: Single channel 2.7Gbps, multi-channel up to 10.8Gbps.

3. Specialized Domain Interfaces: “Specialists” for Specific Scenarios

1. CAN: The “Nervous System” of Automotive Electronics

CAN (Controller Area Network) is widely used in automotive electronics and industrial control, using differential signaling for transmission, supporting multiple master nodes and message priority arbitration, with high reliability and anti-interference capabilities.

Usage Scenarios: Communication between automotive ECUs, control of industrial automation devices.Bandwidth: Standard CAN 1Mbps, CAN FD 8Mbps.

2. I2S: The “Pure Messenger” of Audio Transmission

I2S (Integrated Circuit Sound) is specifically used for audio data transmission, achieving high-precision audio signal transmission through a clock line (BCLK), channel selection line (LRCK), and data line (SD).

Usage Scenarios: Communication between audio codecs and processors.Code Example (STM32 HAL Library):

// Initialize I2S
void I2S_Init(void) {
  // Configure GPIO, clock, I2S parameters
  // ...
  HAL_I2S_Init(&hi2s1);
}

// Transmit audio data
void I2S_Transmit(uint16_t *pData, uint16_t Size) {
  HAL_I2S_Transmit(&hi2s1, pData, Size, HAL_MAX_DELAY);
}

3. HDMI: The Golden Partner for High-Definition Audio and Video

HDMI (High-Definition Multimedia Interface) supports synchronous transmission of high-definition video and multi-channel audio, from HDMI 1.4 (10.2Gbps) to HDMI 2.1 (48Gbps), meeting the demands of 8K video transmission.

Usage Scenarios: Connection between TVs, monitors, and playback devices.Disadvantages: High cable costs; long distances require active cables or converters.

4. Practical Applications and Selection Guide for Interface Protocols

1. Code Example: Basic Applications of UART and I2C

The previous sections have provided basic code examples for Arduino UART and Python I2C, which can be directly copied into the development environment for testing.

2. Timing Diagram Analysis: Comparison of SPI and I2C Communication Timing

By comparing the timing diagrams of SPI and I2C, one can more intuitively understand the differences between the two protocols:

• SPI: The host actively provides the clock, full-duplex synchronous transmission.
• I2C: Synchronization via the SCL clock line, half-duplex transmission, requiring strict start/stop conditions.

3. Selection Decision Tree: How to Quickly Choose the Right Interface

graph TD;
    A[Determine Requirements] --> B{Transmission Rate Requirements}
    B -->|Low Speed (<1Mbps)| C[UART/I2C/SPI]
    B -->|High Speed (>1Mbps)| D[USB/Ethernet/MIPI/EDP]
    C --> E{Number of Devices}
    E -->|Single Device or Few| F[UART/SPI]
    E -->|Multiple Devices| G[I2C]
    D --> H{Application Scenarios}
    H -->|Peripheral Connection| I[USB]
    H -->|Network Communication| J[Ethernet]
    H -->|Mobile Devices| K[MIPI]
    H -->|High-Definition Display| L[EDP]
    H -->|Automotive/Industrial| M[CAN]
    H -->|Audio Transmission| N[I2S]
    H -->|High-Definition Audio/Video| O[HDMI]

5. Interactive Poll: Which Embedded Interface Do You Use Most Often?

To better understand everyone’s usage habits in actual development, we are launching a small poll:

1. UART
2. I2C
3. SPI
4. USB
5. Ethernet
6. MIPI
7. EDP
8. CAN
9. I2S
10. HDMI
11. Other (feel free to leave a comment)

Come and vote to share your choice, and feel free to exchange your experiences and pitfalls in the comments!

6. Summary and Recommended Advanced Resources

Core Interface Protocol Comparison Table

Interface	Typical Bandwidth	Communication Type	Number of Devices	Typical Scenarios	Real-Time Performance	Protocol Complexity
UART	1200bps – 1Mbps	Asynchronous Serial	2	Debugging, Simple Sensors	Moderate	Low
I2C	100kbps – 3.4Mbps	Synchronous Serial	Multi-Master Multi-Slave	EEPROM, Sensors	Moderate	Medium
SPI	Several Tens of Mbps	Synchronous Serial	1 Master Multi-Slave	Flash, ADC	High	Medium
USB	12Mbps – 40Gbps	Synchronous Serial	1 Master Multi-Slave	Peripherals, Storage, Video	High	High
Ethernet	10Mbps – 10Gbps	Packet Switching	Multi-Node	Network Communication, Industrial Equipment	Moderate	High
MIPI	Several Gbps	Synchronous Parallel	1 Master 1 Slave	Mobile Device Cameras/Displays	High	High
EDP	Several Gbps	Synchronous Parallel	1 Master 1 Slave	Embedded Displays	High	Medium
CAN	1Mbps – 8Mbps	Asynchronous Bus	Multi-Master Multi-Slave	Automotive, Industrial Control	High	Medium
I2S	Several Mbps	Synchronous Serial	2	Audio CODEC	Very High	Low
HDMI	10 – 48Gbps	Synchronous Parallel	1 Master 1 Slave	High-Definition Video/Audio	High	Medium

Advanced Learning Resources

• Books: “Embedded System Interface Technology and Applications”, “USB 3.0 Developer’s Guide”Recommended Reading:
• [Efficient Writing Techniques] What is the Use of Quality Scores? How to Improve Quality Scores
• Practical Calculation of Driving Resistance Model Parameters for New Energy Light Trucks: From National Standard Testing to Range Optimization
• Comprehensive Analysis of National Standard GB/T 12536-90 Gliding Test: Accurate Calibration of Driving Resistance Model Parameters for Pure Electric Light Trucks
• Comprehensive Analysis of New Energy Vehicle Brake System Modeling – From Theory to Engineering Applications

If you find this article helpful, feel free to like, bookmark, and comment! Follow me for more embedded development insights, and let’s grow together on the path of technology!