VIDEO How does a USB keyboard work?

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How does a USB keyboard work? In the realm of computer peripherals, understanding the functionality of USB keyboards provides insight into how data is transmitted between devices. The YouTube video titled "How does a USB keyboard work?" dives deep into the technical specifics, comparing traditional PS/2 keyboards with modern USB interfaces.

Key Takeaways​

1. Basic Functionality:
   • USB keyboards utilize a four-pin standard connection—two for ground and power (5 volts) and two for data signals. Unlike older PS/2 keyboards that utilize a simpler protocol, USB keyboards communicate using a more complex signaling system through differential pairing of data lines (D+ and D-).
2. Signal Processing:
   • When a USB keyboard is connected, it signals its speed capability (low speed at 1.5 Mbps or full speed at 12 Mbps) based on the levels of the D+ and D- lines. This connection is crucial for understanding how the computer can differentiate device speeds and manage data flow efficiently.
3. Polling Mechanism:
   • One significant aspect highlighted is the "polling" process of USB keyboards where the computer initiates communication. Unlike PS/2 keyboards that send signals immediately upon key presses, USB keyboards require the computer to request information from the keyboard. This introduces latency—approximately every 16 milliseconds for low-speed devices, which can be a considerable delay compared to the instantaneous response of PS/2 keyboards.
4. Data Transmission:
   • USB keyboards encode data in packets. For instance, when a key is pressed, multiple bits are transmitted, detailing not just the key pressed but also the state of modifier keys (e.g., Ctrl, Alt). The use of NRZI (Non-Return-to-Zero Inverted) encoding is essential for ensuring data integrity and managing clock recovery—a process critical for maintaining the accuracy of data transmission.
5. Latency Comparison:
   • The video compares latency between the two types of keyboards, noting that while USB keyboards at full speed may mitigate some latency issues, cheaper USB keyboards might lag significantly behind their more robust counterparts. This shows that, under certain conditions, traditional PS/2 keyboards could still have advantages over USB, particularly in time-sensitive applications such as gaming.
6. Practical Insights:
   • Analyzing oscillographic data allows for a better understanding of how USB communicates via the differential signals and how effective this method is in noisy environments. This differential signaling helps minimize the effects of electromagnetic interference, ensuring a cleaner signal.
     

     Conclusion​

     The detailed analysis provided in the video encapsulates the complexity and elegance of USB keyboard technology versus traditional methods. For users on WindowsForum, especially those interested in computer hardware and performance optimizations, this understanding can be crucial. Whether considering equipment choices for gaming or regular use, knowing the impact of keyboard technology on overall system performance is vital.
     

     Engage with the Community​

     What are your thoughts on the differences in keyboard technology? Have you experienced any noticeable latency issues with USB versus PS/2 keyboards? Share your experiences and let's discuss!