Jonty WareingOct 15, 2024

What is the most inappropriate connector with enough pins to support USB-C?

I suggest:

Show threadLexiJul 11, 2025
@jonty Parallel perhaps?
Show threadLexiJul 11, 2025
@jonty well, power delivery doesn't seem to work
Show threadLexiJul 11, 2025
@jonty and dmesg is very unhappy when I try to plug in something more advanced than a keyboard
Show threadMartin LingJul 11, 2025
@lexr @jonty It completes the High Speed chirp negotiation, but fails to exchange actual packets. Which is not exactly surprising, but it's cool that we can see it :)
Show threadKlaus FrankJul 12, 2025
@martling @lexr @jonty why exactly isn't this surprising? Could you elaborate for people not that familiar with the USB spec? Is it because of the frequency or resistance of the wire? Or are some pins not connected?
Show threadMartin Ling

@agowa338 @lexr @jonty For USB High Speed (480Mbps) signalling to work, the D+/D- pair needs to be close to the right differential impedance (90 ohms) all the way along the signal path.

Proper USB cables have twisted pairs of the right geometry to hit that. A random DB25 serial cable from 1993 does not. So the signal bounces around inside the cable and interferes with itself.

However, the High Speed negotiation only involves a 10kHz square wave. So that bit works, but 480Mbps packets don't.

Jul 12, 2025 at 1:00amWeb