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Comment by digi_owl | Hacker News Reader

Frankly the C plug spec seems overly convoluted.

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.

Note that the A-to-C cable may well be able to carry 3A, but it shall never use the 3A C-to-C resistor (what many of the cables he find as faulty does).

Note that all this resistor shenanigans are all independent of the Battery charging spec that has been around for some years, and also the Power Delivery spec that was introduced along with the 3.1 USB spec (can be used for all ports) and the C port spec.

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.

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> 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.

Do 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.

A world with smart cables is a dumb world. I want smart devices/adaptors and cheap dumb cables.

USB 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.

Like dumb parallel port cables? or db29? The good days amirite?

> 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.

After 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.

USB-C does lots of things, including high voltage charging, backwards compatibility, and reversible orientation. Yeah, you could make it simpler, but then you'd have to start giving up some of those features, at which point now you've just reinvented USB-A again.

It's just as complicated as it needs to be. And for godssakes, the pin-out diagram isn't that complicated; it only has 24 pins! There's no excuse for flipping two of them. 24 pins is not beyond the pale of what we would reasonably expect manufacturers to be able to wrap their heads around.

http://bi9he1w7hz8qbnm2zl0hd171.wpengine.netdna-cdn.com/wp-c...

"only" 24 pins? That's still 6 times more than the previous standard...

Have you read the spec on what it actually allows though? The fact that it can do USB 2.0 + USB 3.0/3.1 SS + AltMode + 100W Power (bi-directional) all at the same time is... impressive.

To be fair it's really 12 times 2 to allow the cable to be reversible. USB2 had 4, USB3 had 9. Apples to apples you should compare 8 and 18, but the previous two standards weren't reversible.

The previous standard was USB 3.0 which has 9 pins.

https://en.wikipedia.org/wiki/USB_3.0#Connectors

Parallel scoffs at your measly 24 pins.

https://en.m.wikipedia.org/wiki/Parallel_port

Only 25 pins? Why not 40? https://en.wikipedia.org/wiki/Parallel_ATA

I'll see your 40 pin parallel and raise you an 80-pin SCA connector.

https://en.m.wikipedia.org/wiki/Single_Connector_Attachment

Now this is clearly the pinnacle of cable engineering :)

Oh christ... Those pins are actually different signals? When I bought a nexus phone and looked at the new connector I assumed they were just trying to use tricks to reduce contact resistance or something.

Well, the USB 2.0 pins are mirrored so there is no negotiation needed to orient the plug. The others can be mirrored or not, depending on how it is operating. Negotiation can change the job of several sets of pins.

If you're using the plug to do USB, you only use the pins on a single side. It's also possible to use DisplayPort and USB 2.0 with the pins on one side.

You use the pins on both sides to do four-lane DisplayPort, or DisplayPort and USB 3 at the same time, or Thunderbolt.

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