Forum Discussion

Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
16 years ago

open-drain/open collector type of output

Hi All, This might have been discussed before, but I didn't see a definite answer. I have one IO pins which I wanna assign it to be a open-drain type. I tried to add the following attribute ...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
16 years ago

An open-drain output should be nothing more than a single mosfet with the source connected to the ground. And surely enough, a simple CMOS tri-state gate with D=0 will do just that.

But, and I'm speculating here, an FPGA IOE with it's many features (programable slew rate, programable current strenght, PCI clamp diode, etc, etc) might, somehow, behave a bit differently and Altera chose to add a bit of extra circuitry to make sure it behaves as expected from an open-drain.