I have a Space Encounters PCB with Ram errors I've been fixing and thought it would be nice if the Space Invaders Test Rom available on the web would work for Space Encounters as well. After burning one and trying it out, I found out it kind of does (at least for the ram tests). The main problem is that Space Encounters has a hardware special effect that allows the screen to fade up to an all white screen. When the machine is powered up this is on by default and must be turned off by the program. Since Space Invaders doesn't have the feature it doesn't account for it and the text on the Space Invaders Test Rom is unreadable because of the white screen.
While looking at the code of the Space Invaders Rom in order to fix this problem, I decided I'd learn quite a bit about the hardware / software interaction of the 8080 pcbs by documenting its code.
In order to create the Space Encounters Test Rom, I had to convert the Space Invaders Test Rom for use in TASM, the assembler I use for development. In the process, I cleaned things up a bit and it now can be assembled into an exact copy of the original rom.
To assemble this file:
1. Download and decompress TASM.
2. Save the file in the TASM directory changing the .txt extension to a .asm extension.
3. Type on the command line: tasm -85 -b -f00 si_test.asm
4. The resulting .obj file can now be renamed for use in mame.
5. The .obj can be burnt to a 2716 eprom or (if your board's strapping requires it) doubled and burnt to a 2732 eprom.
In case anyone is interested in my (now outdated) first pass at this (it includes the op codes and memory addresses):
Here it is: Original Space Invaders Test Rom Documented
Here is the zip containing the original binaries ready for burning to eproms: Space Invaders Test Rom
The Space Encounters test rom is now completed and can be found here.
Frederic Rodo has modified the space invaders test rom to add the following features:
These mods make the test rom more useful and easy to use. Thanks Frederic!
He has given me permission to distribute it and can be downloaded here:
Note: To emulate the rom in mame rename the file test.h to invaders.h.