Disable Pull up

I don't sure to undestood your question but using the M0-M1-M2 pins is not the right way to do what you want?

Regards Giuseppe

"master" ha scritto nel messaggio news:iMM5b.292163$ snipped-for-privacy@twister2.libero.it...

excuse me for the little clear english. I reformulate the question.

I use tool ise 4,1ì, family spartan2 and language vhdl . When I synthetize a project that uses internal buffer tristate (tbuf), Pull up component have been connected to buffer output for default. I would want to disable this option and to put on the buffer output some pull up or pull down to my choice. Does some environment variable or some procedure exist in order to make that?

thanks

- I don't like to insert directly pull-up in VHDL source file, because pullups in the pads are technology dependant. But I put that in the UCF file by : ############################ ## PULL RESISTOR DESCRIPTION ############################ NET your_padname PULLUP ; NET your_padname PULLDOWN ;

So, remove all pull-ups and pull-downs in your source file and add what you need in the UCF.

Laurent Gauch

- I don't like to insert directly pull-up in VHDL source file, because pullups in the pads are technology dependant. But I put that in the UCF file by : ############################ ## PULL RESISTOR DESCRIPTION ############################ NET your_padname PULLUP ; NET your_padname PULLDOWN ;

So, remove all pull-ups and pull-downs in your source file and add what you need in the UCF.

Laurent Gauch

Hi,

In Spartan-IIe Pull-up resistor on internal Tri-state net is unavoidable as by documentation. It should be the same in Spartan-II. Please correct me if it is wrong or not the same.

Andrey

Spartan-II internal tristates are different than Spartan-II IOB tristates.

IOB tristates to the outside world have user programmable pullups.

Spartan-II internal tristates are tristate emulators, not actual tristate lines. I'm having trouble finding the datasheet reference, but the behavior is "like" there is a pullup with strong low drivers. When there are no drivers, the state is high. When there are multiple drivers with conflicting states, the part does not smoke but instead gives a logic low. If you need a logic low when there are no drivers, either add the additional circuitry to drive a logic low when no selects are active *or* invert the logic so your re-inverted TBUF defaults to low when there are no drivers and settles conflicts with a logic-high.

not

"John_H" ha scritto nel messaggio news:nK26b.35$ snipped-for-privacy@news-west.eli.net...

What happens if you use VHDL's resolved signals (i.e. specifying at HDL level the behaviour of bus conflicts)? It is automatically added something like you described, or resolved signals are just for simulation and don't work with "real" devices?

I have invert logic of the buffer drive, but he is not changed null. then I have realized a component that, when the buffer is in tristate mode,it imposes the intentional level.it works correctly.

Regards Fabrizio