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I have a USB-C flash drive and I'd like to access the data on it using a laptop with an USB-A 3.0 port (a Surface Pro 4). https://plus.google.com/+BensonLeung/posts/UFCHbSDRa2o seems to be saying that it is impossible to have a compliant USB-A female to USB-C male adapter cable, and Leung comments that this product is non-compliant: https://www.amazon.com/dp/B019HWA79A/ref=psdc_464394_t1_B011NNGX9O

What is the best way to use a USB-C flash drive from a laptop with USB-A port (short of using another computer with a USB-C port, obviously)?

  • Hardware recommendations are not on topic, so asking for a specific model, is going to be taken as a hardware request – Ramhound Nov 20 '16 at 23:17
  • No, this is a request about forward compatibility between older Type-A host and newer Type-C plug. – Ale..chenski Nov 21 '16 at 18:59
  • @Ramhound The question sounds pretty general to me, not specific. It is about whether a conversion between USB 3.1 Type C and USB type A will work. – yoyo_fun Nov 21 '16 at 19:17
  • @yoyo_fun, saying "USB 3.1 Type-C" is not sufficient to describe/define the problem. You should differentiate between USB Type-C receptacle, and USB Type-C male plug. The plug has no intelligence to determine connect polarity. All Type-C intelligence is built into C-receptacle. The flash drive is essentially a male plug, and proper connection would require an intelligent C-receptacle, which Type-A port does not have. That's why there is a problem, and questions arise. – Ale..chenski Nov 21 '16 at 19:29
  • @AliChen the question literally wanted a list of hardware that was compatible. – Ramhound Nov 21 '16 at 19:34
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The female-Type-A legacy cable to male Type-C is a legal cable assembly, per spec. I think it is a misprint in the question.

However, adapting the new Type-C device plug to legacy Type-A host port is indeed a challenge, and it is not addressed by specifications. Although there are Type-A receptacle to Type-C plug adapter dongles (as referenced in the question), they cannot provide one of main benefit of Type-C connector, the universal polarity of it. The other problem is that the simple passive dongle will provide always-on VBUS, which is against Type-C mode of operation. Other than that, they should work if nicely implemented, you just would need to flip the Type-C connection in 50% cases to get USB 3 speeds, and the USB2 should always work.

The right way to connect a Type-C flash drive to a legacy Type-A host port is to use a proper hub, with legacy type (A or B) of connector upstream, and full-blown Type-C receptacles on downstream ports. Recently Genesys Logic announced such hub controller chip, GL3523S, as well as others like Microchip and Cypress, but at this time it is difficult to find any OEM products with these chips yet, only development boards are available. If you should find a finished OEM product of this kind, please post.

  • Actually, a passive adapter switch from Type-C port to legacy Type-A port is feasible too, but it would require an active Type-C-compliant polarity management logic, and a high-speed analog multiplexer. I doubt that these kind of dongles exist, they must be too costly to make. – Ale..chenski Nov 21 '16 at 19:20
  • I upvoted the answer. A couple of suggestions to make it even better. 1) Add a sentence or two to the middle paragraph explaining the flip issue (what the problem is and why). 2) The hub solution in the last paragraph--it sounds like you're saying that this is a theoretical solution; you aren't aware of an existing product? So the bottom line is that the only current OTS solution is an adapter, and you may need to flip the connector if it doesn't work? If that's a correct reading, you might want to highlight the actual solution so it isn't lost in the answer. – fixer1234 Nov 22 '16 at 3:23
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    @fixer1234, thanks. I added a clarification about flips, and provided a link to a demo board as a possible legal solution, instead of illegal dongle. If OP will use the dongle only as an adapter to his flash drive and will not attempt to experiment with some arbitrary connectivity, there is no harm. – Ale..chenski Nov 22 '16 at 3:49

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