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Alien Syndrome (Arcade)

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Title Screen

Alien Syndrome

Developer: Sega
Publisher: Sega
Platform: Arcade (Sega System 16)
Released internationally: 1987
Released in JP: April 10, 1987


DebugIcon.png This game has debugging material.


Alien Syndrome is a top-down fast-paced action game where players must rescue hostages while shooting at aliens.

Object Display

AlienSyndromeArcade ObjectDisplayScreen.png

This screen is accessible in service mode after the memory test finishes. Normally a branch instruction prevents it from running, but the following patch NOPs it out so it is accessible again:

Set: aliensyn
maincpu.mw@1C60E=4E71
maincpu.mw@1C610=4E71

The object display screen allows you to cycle through sprites (PAT NO), palettes (COL NO), orientation (DIR NO), and adjust the palette color data.

Controls

Input Outside color editor Inside color editor
Up/down Jump to color editor Move to adjacent digit
Left/right Move to adjacent row Move to adjacent digit
Button 1/2 Adjust item by 1 Adjust item by 1
1P Start/2P Start Adjust item by 16 No effect
1P+2P Start Show/hide object size overlay Show/hide object size overlay
Service Exit screen Exit screen

Sprites of interest

There are some Sega characters that make an appearance in the object list.

PAT NO COL NO Description
67B ?? Flicky
67C ?? Pengo
67D ?? Opa-Opa


Character Display

AlienSyndromeArcade CharacterDisplayScreen.png

This screen is accessible in service mode after the memory test finishes. The game sets up a pointer to the code that runs this editor but overwrites it with the game's reset entry point during the memory test. The following patch redirects the branch that skips the object display screen to instead go to the character display screen.

Set: aliensyn
maincpu.mw@1C610=08A8

On this screen character data is grouped into 64 tiles and four groups are displayed for 256 tiles total.

  • Up/Down selects the group's palette to edit
  • Left/right selects the digit to edit of a palette
  • Button 1/2 adjusts the selected digit
  • 1P/2P start advances the grouping by 256 characters

Leftover source code

Fragment of memory test source code at 0x1DCBE:

Return from memory test
* ------ << memory_test >> ------
memotest:
		btst.b	#_TESTSW,SWITCH0
		beq.

Fragment of listing at 0x2BA56:

00961 
00962 *Angle Get to Player (Enemy Bomb) **************************
00963 *		
00964