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Altera_Forum's avatar
Altera_Forum
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14 years ago

CPLD I/O voltage for bidirectional pins

We are using Altera MAX V CPLD “5m160zt100c5n “in of our project.

We are facing issues that when CPLD is not programming IO voltages on Bidirectional data lines are 3.3 V

but when once CPLD is programmed we see amplitude of only 0.5V on those lines.

Is there anything specific constraint to be taken care inside CPLD while driving bidirectional pins? We are making sure,

when data lines are not driven by CPLD it is in floating state.

1 Reply

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    14 years ago

    Do you check the voltage with a voltmeter or with an oscilloscope? If they are changing constantly, the measurement with a voltmeter could give you a bad value.

    What else is connected on those pins?

    Did you try a very simple design that just puts 1 on the output?