Air-Sea Battle disassembly

Subject: Air-Sea Battle disassembly
From: "Dennis Debro" <dennis@xxxxxxxxxxxxxxx>
Date: Tue, 5 Oct 2004 10:56:19 -0700 (PDT)
Hi there,

I'll be on vacation next week so I thought I'd finish this up and post it
before I go. Hopefully this is labeled correctly and makes sense. It does
compile to the exact same ROM (NTSC and PAL) that's floating around the

Some things to note about this game...

This game uses a horizontal positioning routine originally derived by Joe
Decuir. This routine takes an x-position and calculates the horizontal
delta for the fine position and the coarse value needed to reset the
player's position.

The game speeds aren't adjusted for PAL.

The kernel zone height was adjusted for PAL. PAL kernel zones are 3 lines
higher than NTSC.

D4 of SWCHB is set for output in the NTSC version. I assume this was done
to save a bit when calculating missile size based on difficutly setting as
D4 sets the missile to size 2. The problem is when the values of SWCHB are
masked to get the difficulty setting, D4 is set to 0. This causes the
EXPERT missile size to be 0 for NTSC. This isn't used for the PAL version.
An EXPERT setting for PAL will set the missile to size 2 as intended.

It seems RAM locations $91 and $92 are not used.

So of the original 9 we now have...
Air-Sea Battle

which leaves...
Star Ship (partially done)
Street Racer (partially done)
Video Olympics
Basic Math

I started Street Racer because it was done by Larry Kaplan. I haven't made
much progress on it because I need to spend more time playing the game. I
never played this before. Anyone else want to take it on? It looks similar
to Larry's other work.

Blackjack may be an interesting work too as this would be the first time
the 6-digit display was used.

I'm going to stop for a while though. I need the rest and it'll give a
chance for the archivers to catch up :-)

Take care,

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