If you mean Dreamcast,
I don’t know that anybody’s been able to get compatibility to work with DC other than using an MC Cthulu and soldering a DC Common Ground PCB to it.
Frankly, it’s easier to just buy a PS2-to-Dreamcast converter than going through all the extra soldering and mod work. You do need a PS2 PCB or PS2-native joystick for that, though. The Tekken 5 American edition joystick is the easiest (and among the cheapest) PS2-native sticks to find in the US now and a mid-level mod job for people that have the right tools. The other PS2/Hori joysticks are fairly rare and most of them are Japan-only…
Recommended DC PCB’s to use (if you still want to go the mod-route) that are common ground include the Agetec Dreamcast Arcade Stick PCB… Beware you will to have to some plastic cutting in the interior of the TE stick to put the Agetec PCB in. To me, the bigger mess is going to be figuring out how to string the wire bundle around so that it doesn’t keep any of your pushbuttons from working!