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Altera_Forum's avatar
Altera_Forum
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15 years ago

DC Characteristics

In the cyclone II handbook,page 5-4,pin pull-up resistance values will be lower if an external source drivers the pin higher than Vccio.

i don't understand it . Please explain it .

Thanks

2 Replies

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

    The pull-up resistors are implemented by PMOS transistors, exposing a non-linear I/V characteristic.

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

    If you drive the pin at a higher voltage than Vccio, the clamping diode will start drawing current, thus lowering the impedance seen from outside.