Post #3289061

2026-06-07 18:56 UTC

@gsuberland@chaos.social @matildalove@wetdry.world @valpackett@social.treehouse.systems I don't think it's correct. The CC1/CC2 resistors are not just used in the Power Delivery extension, but are also a mandatory part of the USB-C base spec. The use is required. If CC1/CC2 are open circuits without resistors, the USB-C source is required to treat the port as "not connected", as a result no power is applied. See "4.5.1.2.1. Detecting a Valid Source-to-Sink Connection", "Table 4-10 Source Perspective" and "Table 4-11 Source (Host) and Sink (Device) Behaviors by State" of Universal Serial Bus Type-C Cable and Connector Specification (rev 2.0, 2019). Native USB-C devices are expected to include resistors to even be allowed to use USB-C, otherwise it's a completely fair game to get no power at all from a strict USB-C source (USB-A to USB-C cables have resistors built-in). The non-compliant devices creep in exactly because most USB-C sources are not that strict.

Replies (3)

@r@glauca.space 2026-06-07 19:13

@niconiconi@mk.absturztau.be @gsuberland@chaos.social @matildalove@wetdry.world @valpackett@social.treehouse.systems right, a USB-C power source doesn't supply *any* power by default, unless there are resistors however, USB-C ports are required to tolerate being connected to something which *does* > All USB Type-C ports shall tolerate being connected to USB power source supplying default USB power, e.g. a host being connected to a legacy USB charger that always supplies VBUS. so connecting a legacy USB A charger to a USB C charger should not break anything (nor should connecting two USB C chargers to each other)

Open ##3289062
@gsuberland@chaos.social 2026-06-07 19:18

@niconiconi@mk.absturztau.be @matildalove@wetdry.world @valpackett@social.treehouse.systems oh, shit, sorry, I completely misremembered how this works. that's embarrassing.

Open ##3289064
@erincandescent@akko.erincandescent.net 2026-06-07 19:56

@niconiconi@mk.absturztau.be @gsuberland@chaos.social @matildalove@wetdry.world @valpackett@social.treehouse.systems In fact the USB-PD PHYs at each end require the Rp/Rd resistors exist to operate correctly; they modulate the signal on top of the fixed pull

Open ##3289065