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Altera_Forum
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14 years ago

CPLD Weak pull-up resistors during power-up

All,

There is mention in the MAX II device handbook of Weak pull-up resistors during power-up of the device. What I cannot find is the value of these

weak pull-ups, does anyone know what these are ?

I am not referring to the user programmable pull-ups, but the ones which are present on all I/O pins and affect the power up behavior of the CPLD.

Thanks,

Eric

3 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    User programmable pull-ups and those present during power-up are just the same thing.

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    5–4 Chapter 5: DC and Switching Characteristics

    Operating Conditions

    MAX II Device Handbook © August 2009 Altera Corporation

    IPULLUP I/O pin pull-up resistor

    current when I/O is

    unprogrammed

    — — — 300 μA

    So you can drain 300uA max I think before pull-up operation may fail.
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    Thanks for reminding the 300 uA specification. It has been added with later releases of the Device Handbook and I wasn't aware of it when answering the question. Taking the specification strictly, minimum Rpu is 11k during configuration and 5k in user mode with VCCIO of 3.3V. I'm not convinced, that the specification really indicates different resistance values, I'll check it with a MAX II device occasionally. 300 uA is more convenient however, because it allows higher pull-down resistor values for forced low-level.