The USB 2.0 spec: https://eater.net/downloads/usb_20.pdf

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0:00 Intro
0:50 USB electrical interface
4:43 How USB encodes bits and packets
23:41 USB packet contents
29:26 USB vs. PS/2

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Ben Eater

The USB keyboard protocol is compared with the old PS/2 style interface, explaining how each system communicates key presses to a computer. Unlike PS/2, USB uses a differential pair for data signals and a polling mechanism initiated by the computer to check for key presses. Detailed technical aspects of USB, including packet structures, bit encoding, and advantages of differential signals, are discussed. The post explores whether USB introduces more latency compared to PS/2 and concludes that modern USB keyboards, especially those operating at full speed, have negligible latency differences compared to PS/2 keyboards.

How does a USB keyboard work?