Open drain usage with internal pullups

[Altera_Forum]

Is it possible to use the programmable internal pullup for open drain operation, without adding an external pullup? 

 I guess it should work without problems, besides performance. If so, what would be the estimated maximum frequency on Cyclone II devices? I can't find the resistor value on the datasheet. IO standard will be LVTLL.

[Altera_Forum]

As far as I know, the weak pull-up value is identical to value of i/o pin pull-up resistor before and during configuration documented in table 5-3 of DC characteristics, that is 10 to 50 k for LVTTL. I use it e. g. for static inputs as configuration switches, but slow dynamic operation would be also possible. Susceptibility to capacitive coupled interferences should be considered, howevewer.

[Altera_Forum]

Thanks, 

 I didn't know it was the same pullup used before user mode.

[Altera_Forum]

For any strange reason, the datasheets strictly avoid to tell this simple and obvious fact. However, there's a knowledge base entry, that confirms it for Cylone. 

   --- Quote Start ---  The value of the programmable pull-up resistor for Cyclone® series devices in user mode can be found by referring to the Rconf specification in the "DC and Switching Characteristics" chapter of the respective device handbook.  --- Quote End ---