Phoenix (enhanced) freeplay

[philmurr]

James - thanks!

Yes it is possible to do a plug-in module, but there are a few problems...

1) the game uses an 8085 CPU which has a shared address and data bus, which makes things a bit more complicated.

2) the RAM is split over 2 address ranges (ok that one isn't too difficult)

3) there are 2 separate RAM banks

4) the video RAM directly selects the character ROM

then already you're getting to the stage of a major redesign of the board...

I've actually already written the code for a high score table, but with the original game having only 497 free bytes spread over 38 separate locations and 16 bytes of free RAM space it isn't possible with the existing hardware. I know I've slated the programming and the bugs, but there are clues in there that suggest the original programmers did a lot of code by hand which isn't easy. I still think it's a great game.

So if someone wants to design a plug in that works with the above, also gives an extra area of ROM, and fast RAM that works then that would be very cool and the software is ready to go

 

[RGP]

Hmmm,

You know, when I look at a board for repair, I don't actually consider a lot of this, I follow the signal pathway and interpret what's wrong and fix that so a lot of games i've done including Phoenix I don't give a second thought to share address/data bus - what a pain in the a$$.

Ok, i'll have to take a look at the schematic myself - there must be a chip we can tie a pin to to bank in an extra ROM and RAM chip somehow similar to some of the Pac-Man mods out there.

IIRC, the souza high-score kit requires you solder to an LS139's spare Q output which modified code then tells the CPU to drive that chip to get that signal and hey-presto a different RAM region appears on the bus.