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Thread: USB - Why do I need the 2nd USB (Teensy 4.0 ,4.1) to run an USB Host

  1. #1
    Junior Member
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    USB - Why do I need the 2nd USB (Teensy 4.0 ,4.1) to run an USB Host

    Looking at the datasheet of the 1062 both USB seem to be the same electrical "things".
    Only the shematic of the teensy 4.0 or 4.1 shows a difference in outside connection.
    So VUSB und GND of USB 1 can be used as power supply whereby USB can put power on VUB (4.1).

    But would it be possible to use USB1 as a host port if I seperate VUSB after programming?
    I know this is a therotecial issue but what tells the teensy that USB 1 is a client? Is it the bootloader?

    Thanks for the info!

  2. #2
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    Because there is no software that would drive the 1st as host. No it's not the bootloader - it's just the existing core software.
    Yes, you can rewrite the existing code.

    Not sure if it's worth it - all you save is the header.

  3. #3
    Senior Member PaulStoffregen's Avatar
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    Yes, both ports have hardware which can run in either host or device mode. So is it "only" software and the physical parts on the PCB which make USB1 a device port and USB2 the host port.

    If you change the host library to use USB1, and you create a special non-standard cable (USB specs say Micro-B connectors are only for device mode) reprogramming is quite inconvenient since you would need to disconnect whatever USB device or hub you've connected and reconnect USB1 to your PC, because the bootloader only supports USB1.

  4. #4
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    Thank you all guys for reply,
    thats what I kept somehow in my mind.
    Changing from Arduino to Teensy I was happy to find a board with integrated host.
    For my mini-project I only need one USB-Host and some digital IO ports, but it should be small in size.
    The 4.1 offers too much (card reader) which also needs space and the 4.0 is not available without headers since 4 month and there I would also need additional electronics. (Best for me would be a 4.0 with 2 USB plugs (programming-1 and host-2) on board )
    So the idea was to get a smaller teensy board and "reuse" USB1.
    Youre right, this would mean a lot of other stuff to handle, and I never was good in soldering and handling such tiny hardware also its expensive now to get electronic parts since they have stopped import from china to europe by adding high toll

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