Asteroids Deluxe turbo goals

I've had some confusion over what I'm trying to do with my Asteroids
Deluxe "turbo" hack, so I thought I'd describe it here.

The first thing I wanted to do was to work with more code space than the
standard $6000-$7fff on all 3 games (Asteroids, Deluxe, and Lunar
Lander). I needed the 7400 chip hack to take in to account A15 and
!PMEM. Fortunately Atari provided a couple of pads to "enable" A15
watching so that the other decoders wouldn't mirror everything from 0-7fff
to 8000-ffff. Jumpering the A15 pads causes the LS139 @ E3 to become
selectively active rather than always active. So I needed logic to qualify
A15 and !PMEM - !PMEM For the $6000-$7fff and A15 for $8000-$ffff. 'Cept
it needed to be one signal for !CE.

BTW, I am *NOT* going to bank switch the main program ROM. I *HATE* bank
switching for a variety of reasons. With technology of this era so cheap
these days, it's crazy not to put this all in one ROM image. Plus, I hate
burning a bunch of different images, and I already have code that'll
relocate. Though I might consider bankswitching a 27c040 or something like
that for a TON of vector gaming fun. ;-) But that'd be for a good reason,
and there's really no way around it with a CPU with a 16 bit address
space.

But with the vector ROM(s) my goal is twofold:

* Increase the size of vector ROM region from the stock board
* Combine the vector ROM into one big ROM image (27128)

Right now, RAM is mapped from $4000-$47ff, and ROMs go from $4800-$57ff.
The $5800-$5fff is decoded, but there's no ROM socket for it. The vector
generator circuitry has a 2K address space, so there's no reason it
wouldn't work. So I want to have a *SINGLE* EPROM that allows me to bank
between four 4K images. Granted, the ROM will not be mapped to
$4000-$47ff, but it'd be good to map it from $4800-$5fff.

So I need to use an inverter on the !VRAM signal, so when it's not
accessing VRAM, it's accessing EPROM. That's how it works currently.

In addition to this, I need some way of setting two latched bits on the
27128 to indicate which 4K page in the 27128 I want. Since there's nothing
mapped to the $8000-$ffff when a write occurs, I was thinking the best
thing to do is connect an 8 bit latch and appropriate circuitry to the bus
so I can program those bits.

Another option is qualifying a write cycle to the switches or something
else that's read only.

Any thoughts/techniques/recommendations? Is the 374/245 combo the correct
thing like others suggested?

Of course, as I stated earlier, my findings/tweaks/mods will be posted for
all to download/tweak and play with.

I'm also thinking of doing original games, too, and this gives me a LOT of
growing room.

-->Neil

-------------------------------------------------------------------------------
Neil Bradley Play a song wrong once and it's a mistake.
Synthcom Systems, Inc. Play a song wrong twice and it's Jazz.
ICQ #29402898

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Received on Wed Apr 25 15:58:03 2001