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

--- Quote Start ---

Open drain is a regular tri-state output, that uses the states '0' and 'Z' only.

--- Quote End ---

Actually, most FPGA and CPLD families have a dedicated Open Drain configuration control. See the IOE structure diagram.

I'm not sure what is the purpose of this Open Drain configuration, when it is not strictly needed. In most cases it won't even save user logic.