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Using USB3 and USB2 simultaneously?

ajo115

Hello,

I have been reading up on some of the nuances of using USB in a moto mod.  Specifically, it appears as though it may be possible to use both USB3 and USB2 simultaneously through the moto mod interface, which is normally not a supported use-case.  Normally a USB3 compliant device is supposed to provide the relevant D+/D- signals needed to negotiate back to USB2 if something goes wrong with USB3 enumeration...but the way that the USB3 and USB3 signals are separated out, and the fact that USB2 only supports host mode, and the fact that the USB3 port supports OTG so that the moto mod itself can be a USB host (and the phone the device) makes me think it may be possible to hook one USB device up to the USB2 host port in the moto mod interface (via High Speed Group A signals), and a second USB3 device up to the USB3 host interface (via High Speed Group B signals).  Thus, two USB devices could effectively show up to the Moto phone.

 

Can anyone confirm if my understanding here is correct?  Or, alternately, help me understand how the phone USB host manages the separate USB3 and USB2 interfaces?

 

Thanks much.

  • As far as I know, concurrent USB 2.and USB 3 is not supported. It was mentioned earlier here

  • in reply to kingstu

    Thanks for the quick reply...that previous post is interesting.  They seem to be asking about getting standard USB3 compliant functionality (i.e., if USB3 enumeration fails, falling back to USB2 functionality).  This is different from what I was asking, but good to know that the super speed lines and the high speed lines can't be mixed to form a compliant USB3 interface supporting USB2 fallback.

     

    Can you (or anyone else here) offer any insight as to what the intended use case is for having the USB2 interface (host only) available, along with the USB3 interface (host or device) available?  Is the expectation that a moto mod would either a) need a USB3 super speed interface only, or b) need a USB2 high speed interface only?

     

    Thanks again.