I/O pullup ohm value

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#1
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Hello freaks,

In the datasheet they talk about optional internal pull-ups of the I/O pins when configured as inputs, but I couldn't find their value. Can anyone please tell me where can I find that? I ran through the I/O section and the electrical characteristics, maybe I missed it...

thx,
axos88

axos88

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In case of ATmega48 the datasheet mentions RPU=20-50K (section DC-characteristics)

/Martin.

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Might depend on the chip, but if you consider the Mega48/88/168 for example, see "Typical characteristics -> Pin Pull-up"; p308-309 in my copy. OK, these graphs show pull-up current vs. input voltage, rather than a specific resistor value, but calculation of the equivalent resistance is trivial. Btw. IIRC the "pull-up resistor" isn't really a resistor, but rather a FET, which makes sense since some sort of switch would be required to turn it on/off in any case.

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Well, I need 5k pullup, so I guess i will need an external pull-up anyways

EDIT: Yeah I found it under the typical characteristics, it's 25k, so I will need an external one. Thanks for your answers.

axos88