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USB device / alternate signal functions

Dietmar Eberhard
Prodigy 20 points

Other Parts Discussed in Thread: RM48L952

Hi,

we want to use the USB2 peripheral on RM48L952 as a host, however, the signals USB2.OVERCURRENT and USB2.PORTPOWER cannot be used as we need the alternate peripherals of these two signals.

My question:
Is USB still working, if the mentioned two signals are used by alternate functions?

Thank you for your help.

Best regards
Dietmar

  • 0
    TI__Intellectual 1325 points

    Hi Dietmar,

    USB2.OVERCURRENT: The USB port would work, but you give up the over current protection feature. In the port configuration, NOCP (NO Over current protection) and NSP (No switching power) bits should  be left at default of '1'.

    USB2.PORTPOWER: Since this o/p is connected to the transceiver enable, the transceiver should have an alternate enable signal. 

    In summary, the USB host interface would work, with the above mentioned points to be kept in mind.

    Regards,
    Diwakar

  • 0 in reply to Diwakar Bansal
    Prodigy 20 points

    Hi Diwakar,

    Thank you very much for your answer.

    Concerning USB2.Overcurrent, everthing is clear.

    Concerning USB2.Portpower, I think your answer is correct, if you use USB2 in device mode. Here you need the GZO-signal connected to the USB transceiver , which shares the same pin as USB2.Portpower.

    However, we would like to use USB2 in host mode and thus I think, USB2.TXEN, USB2.Speed, USB2.SUSPEND, USB2.RCV, USB2.TXSE0, USB2.TXDAT, USB2.VP and USB2.VM are the interface signals we need.

    Regards
    Dietmar

  • 0 in reply to Dietmar Eberhard
    Prodigy 200 points

    If you are using USB2 port and want to swap between HOST and DEVICE mode of operation you will have to do some external multiplexing as per the evaulation card schematic.

    Alternatively, as suggested you could use another GPIO output or strap the input ot the perihperal device - and thus lose some functionality.

    This is because the GZO and Port Power Enable are on the same pin for USB2 port.

    GZO is used as a transmit enable for DEVICE mode and Port Power enable is used as a 5V power enable for HOST mode.

    Generally the multplexing of pins is tricky and means you cannot use all of the uP at the same time.

    Best wishes

    Peter