How does a USB keyboard work?

Introduction

This tutorial explains how a USB keyboard functions, based on the insights from Ben Eater's video. Understanding the USB electrical interface, encoding methods, packet contents, and comparisons with other keyboard types can enhance your knowledge of computer peripherals and their operation.

Step 1: Understand the USB Electrical Interface

• USB (Universal Serial Bus) is a standard for connecting devices.
• The USB keyboard communicates with the computer using a specific electrical interface.
• Key components include:
  • Data lines: Two wires (D+ and D-) for data transmission.
  • Power supply: Provides 5 volts to the keyboard.
• Practical Tip: Ensure your USB keyboard is connected to a powered USB port for optimal performance.

Step 2: Learn How USB Encodes Bits and Packets

• USB sends data in packets, which are structured units of information.
• Each packet contains:
  • Start bit: Indicates the beginning of data.
  • Data bits: Actual information being sent, typically 8 bits.
  • Stop bit: Marks the end of data transmission.
• Encoding methods include:
  • Non-return to zero (NRZ): A binary encoding scheme used for efficient data transmission.
• Common Pitfall: Ensure your keyboard is properly connected; otherwise, data may not be transmitted correctly.

Step 3: Analyze USB Packet Contents

• USB packets consist of multiple fields:
  • Packet type: Specifies the kind of data (data, acknowledgment, etc.).
  • Address: Identifies the destination device.
  • Checksum: Ensures data integrity by checking for errors.
• The structure allows for reliable communication between devices.
• Real-World Application: Understanding packet contents can help troubleshoot connection issues with USB devices.

Step 4: Compare USB with PS/2 Keyboards

• USB vs. PS/2:
  • USB keyboards are more versatile and widely used for modern systems.
  • PS/2 keyboards, an older standard, have specific limitations such as only allowing one device per port.
• Advantages of USB:
  • Hot-swappable: Can be connected/disconnected without restarting the computer.
  • Better power management and data transfer speeds.
• Practical Tip: If using older systems, be aware that they may only support PS/2 connections.

Conclusion

In summary, understanding how a USB keyboard works involves grasping the electrical interface, encoding of bits and packets, and the structure of USB packets. Additionally, recognizing the differences between USB and PS/2 can help in selecting the right keyboard for your needs. For further exploration, consider reading the USB 2.0 specification linked in the video description or experimenting with different keyboard types to see how they perform in various scenarios.