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Altera_Forum's avatar
Altera_Forum
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17 years ago

CIII device driving user I/O to low.

Hi all,

I am using Cyclone III device and in I/O assignment, I assigned

Pin L3 as INPUT and is pulled up to 3.3V with an external 20kohm pullup resistor. After reconfiguration of the device(enter user mode), I measured about 1 V on that pin. Looks like the device is driving it low. Then, If i remove the signal from the pin then it goes to 3.3 Volts. What could possibly happen and anyone knows how can I fix this problem? thanks in advance.

best regards,

konyemko

4 Replies

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

    Cause you didn't mention the exact device, I can't check if it's a pin with particular features. But it doesn't sound like normal I/O pin behaviour.

  • Altera_Forum's avatar
    Altera_Forum
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    17 years ago

    sorry,

    the device is : EP3C16F256C6

    please help if you have any idea. Thanks in advance.

    regards,

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

    It's a regular I/O pin. There must be some other condition not said in your post. Are you sure that it's 1V DC? Or did you enable bus-hold for the pin?

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

    Default levels for this device are 2.5V. If you are driving 2.5V you will sink current into your pin. Make sure your pull-up is really 20kohm...a smaller resistor value could result in lots of sink current. Also could be contention. Try removing the resistor and see if you can drive the output to full scale.