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Altera_Forum
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14 years ago

Programmable pull-up resistor in Cyclone II

Dear Sir,

I've a question about the pull-up resistor. Suppose, the pull-up resistor

is related to the I/O voltage Vccio and current strength, isn't it? Why does

it show the resistor is about 10KOhm to 50KOhm in the table5-3 of Cyclone

II Device handbook chapter 5?

For example, Vccio=3.3V, Current strength 16mA in Default of LVTTL.

The pull-up is supposed to be around Rpull-up = (3.3/16)KOhm, isn't it?

Regards,

Peter Chang

7 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    --- Quote Start ---

    Suppose, the pull-up resistor is related to the I/O voltage Vccio and current strength.

    --- Quote End ---

    It isn't. The value is fixed, but subject to PVT (process, voltage, temperature) variations.
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    Dear Sir,

    But I could see a similar example from the page of 8-3 to 8-5 in the MAXII Device Handbook, max2_mii5v1.pdf. It is for the REXT. It, however, is able

    to be used for an internal resistor, RINT, isn't it?

    Regards,

    Peter Chang:confused:
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    In the device handbook, the minimum value for an external pull-up resistor is calculated. The internal pull-up resistor is in contrast a weak pull-up with a resistance several orders of magnitude above this minimum value.

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    Dear FvM,

    Why do we need both? Suppose, we need only either internal or external

    resistor, needn't we?

    Peter Chang
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    They each serve a purpose. The extern pull-up discussion e.g. has the title max ii device compatibility with 5.0-v cmos devices.

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    Dear FvM,

    Do you mean the example is only more like a voltage shiffter? Can the pull-up resistor not be calculated in the same way as the example?

    Thank you!

    Peter
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    The example is in fact for Multi-IO voltage respectively level conversion, it uses the MAX II output in open-drain configuration. In the example, a minimum value based on the available output current is calculated. But in an application, a higher value may be appropriate.