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Jack_Lin's avatar
Jack_Lin
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5 months ago
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Bidirectional pin USB_RX with a pseudo-differential I/O standard must use the OEIN port of the node

I am trying to make a bidirectional differential line using Cyclone V. In VHDL, I set USB_RX, USB_RXn as INOUT on the top level (they are assigned to a Differential SSTL-II 2.5 pair).  I used the AL...
Generic Io
Programmable Logic Device
  • FvM's avatar
    FvM
    5 months ago

    Hi Jack,

    not quite clear what you want to achieve. USB (both FS and HS) is a half-duplex protocol and involves push-pull drivers with enable signal.

    Regards Frank

FvM's avatar
FvM
Icon for Super Contributor rankSuper Contributor
5 months ago

I see same "must use the OEIN port" error when OE is stuck to '0'. OE_B isn't used at all  when driving a differential I/O standard.

Jack_Lin's avatar
Jack_Lin
Icon for New Contributor rankNew Contributor
5 months ago

Thanks.  My original idea was to build it up and set it to input/output first to make sure that it compiles before I add more logic to change the directions.  But it seems like the reason I am getting the errors is because the differential pins on Cyclone V are not bidirectional and can only get set to either input or output.  Will need to check for a different device.