800 with CTIA: What now?

[boxpressed]

I just took possession of my first Atari 800 ever. I already have an 800XL and XEGS (and sold a couple of 400s), but I was hoping that the 800 could take over as my main 8-bit computer because it's so, well, iconic.

 

However, I didn't know about the CTIA / GTIA versions. I'm almost positive mine has the CTIA. It has the sticker on the case bottom that says 16K, the PEEK command doesn't turn the screen black, and my SALT cart returns "Not GTIA" when I run the ITIA diagnostic.

 

I also think that it may have a 64K memory upgrade because it was listed as such and the photo has what looks like a bare memory board in one slot. However, I don't even know how to open the case to get to the memory. When I open the cartridge door, I do see a couple of screws.

 

My question is, what now? I've been reading that the CTIA chip is desirable just to have on its own, but I'm guessing that I shouldn't rely on this unit to play games. Thanks for any advice.

[Tempest]

My question is, what now? I've been reading that the CTIA chip is desirable just to have on its own, but I'm guessing that I shouldn't rely on this unit to play games. Thanks for any advice.

Pretty much. The CTIA chip is an older version of the GTIA and has compatibility and color issues with some games. It's interesting from a history and rarity standpoint, but not from a gaming standpoint. If you don't want it for its historical value, I'd sell it to someone and get a normal GTIA 800.

[Rybags]

The chip change is a straight swapover. CTIA is desirable as in it's rare / collectable. Compatability issues are few, 99% of games should work, most of the 1% should still work but not look right.

 

Put the Basic cartridge in.

 

POKE 623,64

If the screen stays blue, then it's a CTIA machine.

 

? FRE(0)

If you get under 30,000 then it's definately not a 64K machine.

Edited May 17, 2012 by Rybags

[Bryan]

The only way to get more than 48K on an 800 is with bankswitching so FRE(0) wouldn't detect it.

[boxpressed]

The chip change is a straight swapover. CTIA is desirable as in it's rare / collectable. Compatability issues are few, 99% of games should work, most of the 1% should still work but not look right.

 

Put the Basic cartridge in.

 

POKE 623,64

If the screen stays blue, then it's a CTIA machine.

 

? FRE(0)

If you get under 30,000 then it's definately not a 64K machine.

 

I should have said POKE instead of PEEK. The screen stays blue.

 

? FRE(0) returns 37902. I read that BASIC is unable to recognize more than 40K. Also, SALT 2.05 says 40K, but I don't know if it is like BASIC this way.

 

I'd like to know which games have weird graphics with the CTIA.

[Rybags]

The cartridge overlays 8K so detects 40K.

 

Given the fact it's CTIA, I doubt the owner would have put a 64K module into it. Even then, there's probably 0 games that need 64K rather than 48K on an 800. The banking scheme is different to the one XL uses, so not worth worrying about.

 

Games to try - Koronis Rift (most of the screen), Elektraglide (dashboard), Ballblazer & Rescue on Fractalus (loading screens) - will all look wrong, ie a cheap dithered look rather than extra colour.

 

Plenty of demos use GTIA - the famous old Atari robot demo is one of them.

[boxpressed]

Thanks for the suggestions. Here's a photo of the memory card. It was in the upper bank, and the other banks are standard Atari 16K RAM, 16K RAM, 10K ROM.

[AtariNerd]

There is a chip decapping project, trying to document, preserve and vectorize (build working simulations) various ICs, including those in 8-bit computers, like the Atari series. I think they had a CTIA, but in the process of decapping and photographing, the core had cracked or similar such. Wasn't sure if they had found a new donor or not, but they might appreciate it.

Edited May 17, 2012 by AtariNerd

[+Stephen]

There is a chip decapping project, trying to document, preserve and vectorize (build working simulations) various ICs, including those in 8-bit computers, like the Atari series. I think they had a CTIA, but in the process of decapping and photographing, the core had cracked or similar such. Wasn't sure if they had found a new donor or not, but they might appreciate it.

They already have a successful decap of CTIA. The second attempt worked.

[AtariNerd]

They already have a successful decap of CTIA. The second attempt worked.

 

You are correct.

 

http://visual6502.org/images/pages/Atari_C012295_CTIA_die_shots.html

[ijor]

They already have a successful decap of CTIA. The second attempt worked.

 

Correct indeed. Bob donated the second CTIA, Bryan was the first donor.

 

I never made reverse engineered schematics because imaging of the die layout is still not complete. We are still missing "delayered" (when at least the top metal layer is removed) images. Otherwise it is difficult to be 100% sure about the exact layout below the metal.

 

Nevertheless, I think we figured out the CTIA specific (different than GTIA) logic. The images basically showed that GTIA was just a patched CTIA layout. IIRC, we commented about that in the GTIA decap thread (and probably better to follow up there).

Edited October 8, 2012 by ijor

[SeaGtGruff]

As far as game compatibility, don't some games *require* the CTIA for proper (intended) color artifacting? I'd keep the CTIA computer for those games, and play the rest on a GTIA computer.

[Cebus Capucinis]

"Will It Blend?"

 

[SeaGtGruff]

"Will It Blend?"

 

"If you blend it, they will come (out with a newer chip version that shifts the color signal slightly and makes your artifacted colors different)."

[Synthpopalooza]

Basically, it's games like Jawbreaker that rely on the artifacting, if I remember correctly. You get purple and green on GTIA machines, and blue and brown on CTIA.

[Bryan]

Yeah, but you get different colors on the 1200XL, other XL's, and XE's as well so you just have to treat artifact colors as arbitrary anyway.

 

The colors change every time the chroma buffer circuit is changed and the CTIA differences are because of a shift in the position of high-rez pixels.

[SeaGtGruff]

Basically, it's games like Jawbreaker that rely on the artifacting, if I remember correctly. You get purple and green on GTIA machines, and blue and brown on CTIA.

I don't remember the name of the game (I want to say Choplifter but I'm not sure), but I read there was one where the red, white, and blue of the American flag was done with artifacted colors. And I'm not sure which chip or chip version the Ultima games were designed for, but I know that Ultima III looked like crap on my GTIA XL and XE computers-- the grass and water colors were totally wrong.

[Tempest]

CITA was off the market pretty quickly, so I doubt there are many games designed with CITA artifcating in mind. I'd think the bulk of the Atari 8-bit games were designed for GITA equipped Atari 400/800's since that was the most common system and lowest common denominator. I didn't hear of many companies in the US design games to take advantage of the XL line's abilities.

[a8isa1]

CITA was off the market pretty quickly, so I doubt there are many games designed with CITA artifcating in mind. I'd think the bulk of the Atari 8-bit games were designed for GITA equipped Atari 400/800's since that was the most common system and lowest common denominator. I didn't hear of many companies in the US design games to take advantage of the XL line's abilities.

There were some some early Sierra On-line adventures which provided artifacting examples and let you choose which of the two looks best.

 

I always assumed this was really a selection between CTIA or GTIA machines.