Re: Bizarre Tailgunner (2) Experience

At 04:50 PM 8/20/97 CDT, you wrote:
>
>(was: RE: interesting coincidence..)
>
>In message "interesting coincidence..", you write:
>
>> >I haven't done any ROM comparisons for Tailgunner.
>
>My TG2 originally used 2708s so I converted it to use 2532s by reading
>in the 2708s and combining the images. Once I had figured the original
>addressing and mapped the various locations, I burned the new roms. All
>seemed to be ok as the game powered up and entered the attract mode.
>However, once I started playing the game it was apparent that something
>was very wrong.
>
>First I noticed a small twitch in the approaching enemies. Their movement
>seemed to become more and more jerky, until the ships would actually dis-
>appear from one location and reappear somewhere else. The next major shock
>was to see the enemies start going backwards! As you know they *always*
>move forward. The last oddity was the shield. Instead of being geometric,
>the shield kind of bends into an oval shape. Really weird!
>
>Anyway, my point; thinking I had somehow managed to corrupt my rom images
>I double checked them against the TG roms someone sent me in a file called
>CinemROMS.tar. I don't know if the roms in that file were taken from a TG
>or a TG2. However, the roms from my TG2 compared perfectly with the roms in
>the file.
>
>Incidently, the roms I burned showed the correct checksum and even compare
>with no errors to the rom files. Finally, I burned a new set and they worked
>fine. Although that was years ago, I saved the chips and occasionally put
>them in the game for a laugh. It also helps increase the challenge!

Sounds like you have slow ROMs. The ROM readers read ROMs at an very slow
rate, whereas running them in the game runs them at full speed. It sounds
like some data just can't get there fast enough. So they checksum and
compare ok in the ROM reader but don't play correctly.

It's amazing the game continued to run though, it wouldn't take but one
corrupted opcode to crash the game. There is a table lookup instruction
that allows the game code to access ROM tables, it plays a lot with the ROM
address bus. Maybe your ROMs are just at the verge that allows normal
sequential access to work, but table lookups sometimes get scrambled. Or
maybe I have no idea why your ROMs do what they do and I'm pulling ideas as
fast as I can type out of thin air. If I were a betting man I'd bet on the
latter...
>
>What other really bizarre things have you seen come from a cinematronics game?
>
>> Does anybody with an easily accessible Tailgunner II want to do a ROM
compare?
>
>I have the TG2 files if you want to compare them.

If you compared your ROMs with those on the net, then I'm sure your ROMs
match the standare TG ROMs. 1) It's unlikely that the ROMs on the net are
from a TG2, and 2) If they are from a TG2, then a TG2 matches a standard TG
since I've compared the ROMs from my TG with the ones on the net (actually
many copies of the many differently named ROMs on the net)

So thanks Mark, I think you've answered the TG / TG2 question.

I someone is *really* not convinced, you can send me your images and I'll
compare them with my known TG set, or vica versa.

-Zonn
Received on Wed Aug 20 18:05:39 1997