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9 comments
PattaFeuFeu

@luana @bcoffy Was wondering the same! I have even used one of those for years now to connect a USB-C webcam to the USB-A-only dock of my monitor

medb

@PattaFeuFeu @luana @bcoffy in the USB-C spec it says they're not allowed because "such adapters would allow many invalid and potentially unsafe cable connections to be constructed by users" (e.g. stick two of them onto a USB-C to C cable and you get a USB-A to A cable). they're pretty safe so long as you know what you're doing with them, they just don't want people sticking the wrong things together and breaking their electronics

PattaFeuFeu

@medb
That makes sense. Thanks for the explanation!

@luana @bcoffy

cesarb

@luana @bcoffy Because if you connect two of these adapters together through a normal USB-C cable you end up with a male A to male A cable, which is forbidden because it shorts together the power supply of both ends of the cable (the cursed A-to-A debug cable is allowed only because it doesn't connect the power or USB 2.0 pins, it connects only the USB 3.0 pins).

Kamila Borowska

@luana @bcoffy if female C to male A was allowed then such an adapter could be used to create male A to male A cable

USB was never designed to allow male A to male A, and such a cable could potentially start a fire

Jonas Platte

@xfix @luana @bcoffy I had an external HDD case with (only) USB-A port for a while, which came with an male-A-to-male-A cable... Also got a tiny male-A-to-female-C and male-B-to-female-C cable lyring around πŸ˜„
I don't really understand that explanation but I guess it's also why the latter two items were so hard to find πŸ˜…

Kamila Borowska

@jplatte @luana @bcoffy the way USB is designed, the host device (indicated by using A connector) is supposed to supply power

if both devices decide to supply power you end up with current fight where both device supply 5V power, and the consequences of that could be pretty bad

this is not a problem with USB-C, as USB-C has a way to negotiate who is responsible for supplying the power

USB-C to USB-A/USB-B adapters are fine provided the user doesn't use those to create a male USB-A to male USB-A cable, however the possibility of someone creating those and then causing damage to their hardware (for instance, a less tech-savvy user could try connecting two computers using usb-a to usb-a cable) means that those adapters are forbidden by the spec

as for your external HDD, i assume the manufacturer wanted to save money using USB-A instead of USB-B, USB-C or custom connector as they should be using

@jplatte @luana @bcoffy the way USB is designed, the host device (indicated by using A connector) is supposed to supply power

if both devices decide to supply power you end up with current fight where both device supply 5V power, and the consequences of that could be pretty bad

this is not a problem with USB-C, as USB-C has a way to negotiate who is responsible for supplying the power

Jonas Platte

@xfix @luana @bcoffy
Aha! So my male-B-to-female-C is actually fine then because it doesn't make it easier to make A-to-A connections?

Also *how* forbidden is this really? It seems like A-to-A is pretty simple to obtain. (though then again I've seen something about male-to-male US power cords that you can apparently get easy enough and those *got to be* super illegal to manufacture so maybe simple-to-obtain means nothing)

Kamila Borowska

@jplatte @luana @bcoffy as far the spec is USB concerned they are forbidden. USB-IF will refuse to certify any such adapter

with that said, manufacturing those is not illegal, and there are plenty of smaller companies that will sell those

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