Sorry, I'm not sure what you are trying to do, so I'll need to ask some background questions:
What joystick do you have (maybe u360)? Or are you using an encoder (maybe ipac)?
Are you pressing tab while playing mame?
Or are you running an application designed remap the joystick/encoder? Which app?
The reasons I'm not sure are:
- tab is a mame thing and you can't program the joystick from here (you can do the
opposite though: remap mame to match what the joysticks/keyboards already output), and
- ipac is
programmed with mouse click then key press instead of tab, and
- the
u360 UltraMap doesn't output keys but joystick buttons
Hope we can help you with more info.