Alien Syndrome (Arcade)

Alien Syndrome
Developer: Sega Publisher: Sega Platform: Arcade (Sega System 16) Released in JP: April 10, 1987 Released in US: June 1987 Released in EU: 1987 This game has debugging material.

To do: Unused music

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

Object Display

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

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