Xegs, Changing the internal game.

[Gaetznes]

Long story short.

 

I saw a post about bank swapping the basic and a game on the 1200xl. This made me think about my xegs that I have in my repair pile. That has Missile Command internally installed on the system. So through a series of experimentation, revelations, leading me to eventually pulling out the hex editor. I determined what is partially stated in some of the references I have linked below. The C101687 rom is a concatenated file containing in this order: Missile Command 8KB, RevC Basic 8KB and Rev4 OS 16KB. The xegs C101687 ic is Jedec compatible, meaning I can use a 27c256 eprom (32KB / 32,768 bytes). The concatenated file must be that size, not a byte less or more. So the goal is to change the game. Doing limited testing, I tried multiple different extensions, xex .rom etc. The .rom extension was the only one that gave me limited success. Limited, because not every 8KB game I eventually tested worked. I used a tms27c256 eprom, Hxd as my hex editor, which also works for file comparing and concatenating the multiple files on hand. Some days Command Prompt is just not fun to use. lol.

 

End result is I was able to concatenate my own working file containing Missile Command, RevC Basic and Rev4 OS. Later on, I did the same with Qix, RevC Basic and Rev4 OS. Below are all the references I used. In addition to my own log. That contains every assumption and conclusion made during my experimenting. Whether it was right or wrong, I left it it in my log. Hopefully others can learn from it. Picture below references.

 

 

References

My Mod and repair blog including this : https://www.gatesgames.ca/february-2018.html

Rom sources http://www.atarimania.com/

Basic info http://www.digitpress.com/eastereggs/a48ataribasic.htm

OS/Basic rom source http://atari.vjetnam.cz/index.php?frame=roms

OS Info http://www.ataripreservation.org/websites/freddy.offenga/osroms.txt

OS Info https://www.wudsn.com/productions/atari800/atariromchecker/help/AtariROMChecker.html

IC identification https://www.atarimax.com/jindroush.atari.org/achip.html

Post that triggered my experimentation http://atariage.com/forums/topic/147677-questions-about-1200xl-mods/?&p=1875799&hl=rom+socket&fromsearch=1&do=findComment&comment=1875799

 

[+davidcalgary29]

Very nice! Flashjazzcat swapped out Missile Command for Star Raiders in the XEGS he brilliantly modded for me.

[+DrVenkman]

Cool. [emoji4]

 

One of the fun things about an Ultimate 1MB upgrade is that if you set the “XEGS” jumper on the U1MB and flash an XEGS rom to it, you can cycle between whatever 4 8K roms you want in the “Game” slots. I currently have Missile Command, Pac-Man, Centipede and Galaxian in my daily driver. [emoji4]

[Gaetznes]

Cool. [emoji4]

 

One of the fun things about an Ultimate 1MB upgrade is that if you set the “XEGS” jumper on the U1MB and flash an XEGS rom to it, you can cycle between whatever 4 8K roms you want in the “Game” slots. I currently have Missile Command, Pac-Man, Centipede and Galaxian in my daily driver. [emoji4]

 

That is awesome. Are you limited to four 8KB games? Does a feature exist that allows two 16KB, or one 32KB game?

[+DrVenkman]

 

That is awesome. Are you limited to four 8KB games? Does a feature exist that allows two 16KB, or one 32KB game?

Just four simple 8K slots for XEGS games. Otherwise the U1MB core would have to support various cartridge memory bank switching schemes. Given how much else the U1MB does, that would be asking quite a bit.

[Gaetznes]

Just four simple 8K slots for XEGS games. Otherwise the U1MB core would have to support various cartridge memory bank switching schemes. Given how much else the U1MB does, that would be asking quite a bit.

 

I have been watching youtube videos on the U1MB. That is very amazing. Lost for words on how many features exist on this upgrade.

[+DrVenkman]

 

I have been watching youtube videos on the U1MB. That is very amazing. Lost for words on how many features exist on this upgrade.

 

You can actually cheat a little bit. The four "BASIC" slots in the U1MB can also hold any standard 8K rom. So if you don't want a built-in BASIC, you can actually install 8 games.

 

(In my case, the XEGS game slots are just sort of for fun - I have an UNO Cart and can boot pretty much any vintage game ROM either from there or from an SIO2PC. I use the BASIC slots in the Ultimate 1MB for Atari BASIC revision C, Altirra BASIC, Atari PILOT, and Atari Assembler/Editor).

[lbaeza]

...Doing limited testing, I tried multiple different extensions, xex .rom etc. The .rom extension was the only one that gave me limited success. Limited, because not every 8KB game I eventually tested worked. I used a tms27c256 eprom, Hxd as my hex editor, which also works for file comparing and concatenating the multiple files on hand. Some days Command Prompt is just not fun to use. lol. ...

 

Hi

 

It looks like you have a confusion regarding Atari executable files and ROM files.

You cannnot take an Atari executable (XEX) file, burn it into an EPROM, and try to boot your Atari from that EPROM. It will not work.

You can only do this by using proper ROM cartridge files only. These have usually the BIN or ROM extension.

Finally, burning an EPROM with a CAR file contents will not work also. CAR files are useful for emulators only, they tell it what type of cartridge is the dump contained within the CAR file itself.

 

Regards,

 

Louis BQ

[Gaetznes]

Hi

 

It looks like you have a confusion regarding Atari executable files and ROM files.

You cannnot take an Atari executable (XEX) file, burn it into an EPROM, and try to boot your Atari from that EPROM. It will not work.

You can only do this by using proper ROM cartridge files only. These have usually the BIN or ROM extension.

Finally, burning an EPROM with a CAR file contents will not work also. CAR files are useful for emulators only, they tell it what type of cartridge is the dump contained within the CAR file itself.

Regards,

 

Louis BQ

You are correct, my experience with working with Atari 8bit is extremely limited. I've had to do a far amount of playing around and finding the proper roms with the proper extensions. If you get a chance to read my blog, you will see extensive human error, that leads me to the understanding the distinction between the types of extensions. On a very very basic level. I do appreciate your explanation extensively. As my primary experience with games has been focused on fixing old arcades and Atari 5200, through to the era of Genesis and snes. Building rom hack or import games. Actually working with computers requiring os, basic kernels etc is very new to me. Thanks again

[Rybags]

With some work you could put another filetype, it would need to self-relocate to Ram then run.

With even more work you could in theory get rid of the second character set and Self-Test leaving 11K for a game. Using compression you'd possibly fit a 16K game into the Rom space

 

But IMO more effort than it's worth. If I was to do such a thing I'd probably just put the Atari AsmEd cart as the second 8K and rig the OS to allow Select-Reset to switch between the two.

[lbaeza]

You are correct, my experience with working with Atari 8bit is extremely limited. I've had to do a far amount of playing around and finding the proper roms with the proper extensions. If you get a chance to read my blog, you will see extensive human error, that leads me to the understanding the distinction between the types of extensions. On a very very basic level. I do appreciate your explanation extensively. As my primary experience with games has been focused on fixing old arcades and Atari 5200, through to the era of Genesis and snes. Building rom hack or import games. Actually working with computers requiring os, basic kernels etc is very new to me. Thanks again

Hi

 

Glad to know you took my comments the right way.

Unfortunately I have limited time to post on the forum, so I was not able to explain in detail why it should work or not for you.

Is good to see somebody playing with the Atari at the ROM level, in a similar to what I did not long ago.

Please keep us updated with your findings.

 

Kind regards,

 

Louis BQ