Input/Bidirectional Pads

Discussion in 'Programmer's Corner' started by abhi6teen, Aug 6, 2008.

  1. abhi6teen

    Thread Starter New Member

    Aug 6, 2008
    3
    0
    If IBE of input or bidirectional pad is asserted and input data to the pad is 'Z', then what will be the expected output of the pad?
    Should it be 'Z' or 'X'?

    we are implementing the below logic:
    pad_output = IBE & pad_inpt;

    but this logic will give pad output as 'X' if input is 'Z'. Is this logic correct or it will later cause problem?

    Please assist.
     
  2. roddefig

    Active Member

    Apr 29, 2008
    149
    0
    What behavior do you want the logic to have?
     
  3. abhi6teen

    Thread Starter New Member

    Aug 6, 2008
    3
    0
    I want to know that is it correct to implement this logic that if 'Z' is comming as input then output is X for an input pad?
    or the output must also be Z in this case?
    How it will be affected in both scenarios?
     
  4. abhi6teen

    Thread Starter New Member

    Aug 6, 2008
    3
    0
    can you please now reply on input/bidirectional pads topic...
     
  5. roddefig

    Active Member

    Apr 29, 2008
    149
    0
    Yes. The issue is that you are performing a logical comparison between a value and a "high impedance" which doesn't make any sense. Thus, the output is undefined. The "z" value is not a value in the sense that a 0 or 1 is, it only defines a driver state. You should never see a "z" as an input to a comparison.
     
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