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  1. #1
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    USB Softcore for FPGA

    Have anyone used https://github.com/avakar/usbcore before ?

    why do we need extra resistance on the tx pin ONLY ?

    Whichever pins you transmit on need to have resistors after them. The exact values will depend on the internal resistance of the pins; usually something around 27 ohms will be ok.

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    Re: USB Softcore for FPGA

    Sounds like you need to review the USB spec for required driver impedance.



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    Re: USB Softcore for FPGA

    According to section 7.1.1 (Tx) and 7.1.2 (Rx) of https://usb.org.10-1-108-210.causewa...7.pdf#page=144 , it seems like we need some resistance for impedance matching for BOTH Tx and Rx.



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    Re: USB Softcore for FPGA

    You have been apparently confused by the USB 2.0 spec describing both FS and HS requirements. It's easier to review usb11 spec. For FS as targeted by the FPGA project, the effective driver impedance is 28 to 44 ohm (internal driver impedance + series resistor). There's no receiver termination (except for kohm resistors used for device identification.

    The correct GitHub link is https://github.com/avakar/usbcorev, by the way.


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    Re: USB Softcore for FPGA




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