3 ms·
> Each cable needs one of 3 resistors depending on them being a A/B-to-C cable, 1.5A C-to-C cable, or 3A C-to-C cable. No, for C-to-C connections, the resistan
by teraflop 11y ago
> Each cable needs one of 3 resistors depending on them being a A/B-to-C cable, 1.5A C-to-C cable, or 3A C-to-C cable.
No, for C-to-C connections, the resistance is provided by the host ("downstream-facing") port, not the cable. The resistor in an A-to-C cable is basically emulating the signal that would otherwise be provided by the host.
There's no such thing as a "1.5A C-to-C cable"; all type-C cables are required to deliver at least 5A. The limiting factor is the host, not the cable, which means the cable must not incorrectly advertise capabilities that the host doesn't support.
> Never mind that a C port has so many extra pins compared to a A or B port, that one would think that id-ing a A-to-C cable would have been as simple as looking for life on any of those extra pins.
That's exactly what the new CC pin is used for. Right now the spec says "legacy cables should connect CC via a 56kΩ resistor", but it wouldn't matter if instead the requirement had been "legacy cables should leave CC disconnected"; the issue is that cable manufacturers are ignoring the spec.
- digi_owl 11y agoDo wonder how many others over in China or elsewhere has made the same mistake i have apparently made. 4.11 could really use a massive cleanup for readability it seems.
- knughit 11y agoA world with smart cables is a dumb world. I want smart devices/adaptors and cheap dumb cables.
- wtallis 11y agoUSB cables aren't smart cables by any stretch of the imagination—not when we've got standards like Thunderbolt. A single resistor is not unreasonable complexity on top of the requirements to get the pinout correct.
- jethro_tell 11y agoLike dumb parallel port cables? or db29? The good days amirite?
- legulere 11y ago> There's no such thing as a "1.5A C-to-C cable"; all type-C cables are required to deliver at least 5A. 1.5 A is required to be supported by USB-C, while 3 A is optional. Everything over it is covered by USB Power Delivery, which requires a marking of the cable which of the 5 profiles are supported.
- teraflop 11y agoAfter re-reading the spec, I think both your comment and mine are slightly wrong. Connectors must be capable of handling 5A; cables are required to support at least 3A. (See sections 3.1.2 and 3.7.7.4.) You're correct that higher power requires USB-PD.