|This page is rather stubbly and could use some expansion.|
Are you a bad enough dude to
On the title screen, press B, Left, Up, Right, B after the first alien has popped up to enable a debug mode when a 1-player game is started. It's called, rather appropriately, "DR DAVES CHEAT SCREEN".
Present at offset 1FFDE in the US version is a copyright string and build date:
(c)1990 Activision. 06/28/90 David J. Ross
The European version has an updated version of the string at offset 1FFE0:
(c)1991 Activision. 01/21/91 David J. Ross