What type of encoder do you have?
- A keyboard/gamepad hybrid like the IPac/Mini-Pac/U-HID.
- A gamepad-only encoder like the ZD encoder.
There are three common approaches to using P1 Start + P2 Start as Exit:
1. "Shifted functions" on the IPac. (works with any program that uses ESC as Exit)
2. "UI Cancel" setting in MAME. (only works in MAME)
3. An external program like the Front End or an AHK script that looks for both buttons being pressed and held for a certain length of time then sends an ESC keystroke. (works with any program that uses ESC as Exit)
If you don't have an IPac, that pretty much rules out approach #1.
- If you do have an IPac, you may need to reprogram it. It's
highly unlikely that the flash memory would get corrupted, but not entirely impossible.
If your system uses approach #2:
- Go into the MAME menu system. (TAB)
- Go to "Input (General)" -- "User Interface" menu.
- Scroll down to "UI Cancel". It should be mapped to "1 2" instead of the default "ESC", assuming that you have a keyboard encoder.
- To map both buttons to "UI Cancel", press ENTER then press and hold both buttons.
If your system uses approach #3, we'll need to figure out which FE or AHK script was used.

Scott