Piggy-backing this comment to add some context for the OP video: This "USB device discovery" video is actually the latest in a series of videos where Ben Eater is building a simple 8-bit computer on breadboards. He hooked up a PS/2 keyboard as an input device, and then got sucked into a tangent of investigating and explaining keyboard protocols.
- Somebody on Patreon asked about USB keyboards having higher latency than PS/2, so he made a video about the basic USB protocol: https://www.youtube.com/watch?v=wdgULBpRoXk
- He made the OP video about USB keyboards being limited to holding six keys at once.
- He investigates the PS/2 keyboard protocol: https://www.youtube.com/watch?v=7aXbh9VUB3U
- Somebody on Patreon asked about USB keyboards having higher latency than PS/2, so he made a video about the basic USB protocol: https://www.youtube.com/watch?v=wdgULBpRoXk
- He made the OP video about USB keyboards being limited to holding six keys at once.