Atari 800 issue

[55five66six]

Hi Everyone,

 

One thing that I noticed with my Atari 800 is that for some reason, on select games, the sprites aren't displayed. (PacMan, Ms Pacman, Death Star).

 

Would there be any reason for this? My Atari 400 works just fine with these games.

[BillC]

A possibility is one system may have a CTIA chip and the other a GTIA.

 

The following thread has information on how to determine which chip each computer has: http://atariage.com/forums/topic/80199-atari-800-ctia-or-gtia/

[55five66six]

I just tried the basic program that was used in the example. Both are showing a black screen, meaning that they're both GTIA.

 

 

10 GRAPHICS 9
20 GOTO 20

If you get a black screen, you have the newer GTIA chip. If you get a blue screen, you have the older CTIA chip. Of course you would need a BASIC cart.

The original source of this info

Edited September 13, 2013 by SoilentGreen

[55five66six]

Is there a way my GTIA chip could be fried?

[Rybags]

Are they cartridge games? A bad cart port might cause glitches although generally you'd have the program crash as well.

 

Do you have games that do work? Most commercial games use PMGs which rely on a working GTIA.

[russg]

Is there a way my GTIA chip could be fried?

I suspect your Antic or GTIA. Can you swap them out?

[kenjennings]

Try this. (Works in OSS BASIC XL. I guess it should probably work in TurboBASIC.)

 

200 Poke $d01d,0:Rem GRACTL

210 For I=0 To 4

220 Poke $d00d+I,$ff:Rem GRAF*

230 Poke $d008+I,$ff:Rem SIZE*

240 Next I

250 For I=0 To 3

260 Poke $d000+I,$30+(24*I):Rem HPOSP*

270 Poke $d004+I,$b0+(6*(3-I)):Rem HPOSM*

280 Poke 704+I,I*$20+$22

290 Next I

 

This fires up Player/Missile graphics without ANTIC DMA. You should see colored, vertical stripes on screen. If you do, then GTIA (or at least the internal Player/missile overlay part) is working.

 

If it doesn't work, then ANTIC DMA for Player/Missile graphics is broken, or GTIA's receipt of ANTIC DMA data is broken.

[55five66six]

Hi Ken,

 

All I have is the Basic cartridge that general comes with the Atari 800. Is that the TurboBasic that you're talking about?

[+Stephen]

Hi Ken,

 

All I have is the Basic cartridge that general comes with the Atari 800. Is that the TurboBasic that you're talking about?

No - if all you have is regular BASIC, you will just have to convert the HEX numbers (they start with $) to decimal.

 

I forgot - it needs to be all CAPs too. Here you go:

200 POKE 53277,0:REM GRACTL
210 FOR I=0 TO 4
220 POKE 53261+I,255:REM GRAF*
230 POKE 53256+I,255:REM SIZE*
240 NEXT I
250 FOR I=0 TO 3
260 POKE 53248+I,48+(24*I):REM HPOSP*
270 POKE 53252+I,176+(6*(3-I)):REM HPOSM*
280 POKE 704+I,I*32+34
290 NEXT I

It should produce the following output:

[kenjennings]

Ok, in decimal.... If the Windows calculator is worth anything. it's never been wrong.....

 

200 Poke 53277,0:Rem GRACTL

210 For I=0 To 4

220 Poke 53261+I,255:Rem GRAF*

230 Poke 53256+I,255:Rem SIZE*

240 Next I

250 For I=0 To 3

260 Poke 53248+I,48+(24*I):Rem HPOSP*

270 Poke 53252+I,176+(6*(3-I)):Rem HPOSM*

280 Poke 704+I,I*32+34

290 Next I

 

And remember Atari BASIC only accepts UPPERCASE.

[+Stephen]

Ok, in decimal.... If the Windows calculator is worth anything. it's never been wrong.....

 

200 Poke 53277,0:Rem GRACTL

210 For I=0 To 4

220 Poke 53261+I,255:Rem GRAF*

230 Poke 53256+I,255:Rem SIZE*

240 Next I

250 For I=0 To 3

260 Poke 53248+I,48+(24*I):Rem HPOSP*

270 Poke 53252+I,176+(6*(3-I)):Rem HPOSM*

280 Poke 704+I,I*32+34

290 Next I

 

And remember Atari BASIC only accepts UPPERCASE.

Haha - looks like you beat my update by a few seconds

[55five66six]

OK.. so it looks something like that.. The weird part is that mine is different colored. Where there should be a yellow box, comes up as a green box. All the colors are off from what I see (Darker or just the wrong color)

[+Stephen]

OK.. so it looks something like that.. The weird part is that mine is different colored. Where there should be a yellow box, comes up as a green box. All the colors are off from what I see (Darker or just the wrong color)

Don't worry about the colours being a bit off - as long as everything is displaying, this would show the GTIA is working properly. Very strange that this code would work, but PacMan wouldn't show the sprites. Could be an issue with ANTIC, DMA related. Hopefully one of the resident hardware experts will chime in.

[1050]

Not the expert called for, but I'm thinking that there is an adjustable color coil on the 800 to correct colors with. IIRC you have to go under the hood to get at it, but it might have a hole from the bottom to use similar to the 800XL? You will need either a plastic or fiberglass hex wrench to turn the slug inside the coil, but a metal one will work if you pull it out and then look at the colors. The iron in the allen wrench will totally blow the color off while it's still in the coil. No help on the right size either, sorry.

 

I would adjust the colors to be correct first, your sprites might be the same color as the background - there ARE there, you just can't see them because they are the same color as the background?

[BillC]

Not the expert called for, but I'm thinking that there is an adjustable color coil on the 800 to correct colors with. IIRC you have to go under the hood to get at it, but it might have a hole from the bottom to use similar to the 800XL? You will need either a plastic or fiberglass hex wrench to turn the slug inside the coil, but a metal one will work if you pull it out and then look at the colors. The iron in the allen wrench will totally blow the color off while it's still in the coil. No help on the right size either, sorry.

 

I would adjust the colors to be correct first, your sprites might be the same color as the background - there ARE there, you just can't see them because they are the same color as the background?

The color adjustment pot for the 800 is on the CPU card under the RF shield. There is a hole for adjustment through the rear of the shield which is accessible once the OS/RAM card hatch is removed.

[55five66six]

I don't think the color is the issue. If that was the case, I would see an outline or some sign there are sprites on the screen. When I popped PacMan back in and watched the gameplay, there are no sign of sprites. Just dots disappearing when pacman moves over them.

[+Stephen]

I don't think the color is the issue. If that was the case, I would see an outline or some sign there are sprites on the screen. When I popped PacMan back in and watched the gameplay, there are no sign of sprites. Just dots disappearing when pacman moves over them.

The good thing about the 400 and 800 is all chips are socketed. Honestly, if I were you, I would disassemble both machines, and swap the GTIA 1st, and then the ANTIC. It almost has to be a GTIA related issue, but I don't understand how the BASIC program which overlayed all players and missiles would work, but games would not.

[55five66six]

It's a weird thing, I know. I thought it was just a crazy fluke when I bought the unit.

 

I'll try swapping out the chips and see if that does it. I already saw that Best-Electronics has the GTIA and ANTIC chips for cheap, so I'll buy those and see if it helps.

 

Thanks!

[kenjennings]

but I don't understand how the BASIC program which overlayed all players and missiles would work, but games would not.

 

The test program fired up PM graphics without ANTIC DMA. This appears to work so it means the overlay engine part of GTIA is working. Since the usual method of Player/Missile graphics uses ANTIC DMA to update the bitmap on each scan line this means that either the ANTIC DMA for player/missile grpahics is broken, or GTIA's mechanism to receive the data is broken.

 

Here's a version of the program that starts up ANTIC DMA. It uses the ROM characterset as PM memory, so the vertical bars are now big letters, numbers and symbols....

 

200 POKE 53277,3:REM GRACTL

202 POKE 559,46:REM DMACTL

204 POKE 54279, 224: REM PMBASE (USING ROM CHARACTER SET)

210 FOR I=0 TO 4

230 POKE 53256+I,255:REM SIZE*

240 NEXT I

250 FOR I=0 TO 3

260 POKE 53248+I,48+(24*I):REM HPOSP*

270 POKE 53252+I,176+(6*(3-I)):REM HPOSM*

280 POKE 704+I,I*32+34

290 NEXT I

 

[Joey Z]

It's a weird thing, I know. I thought it was just a crazy fluke when I bought the unit.

 

I'll try swapping out the chips and see if that does it. I already saw that Best-Electronics has the GTIA and ANTIC chips for cheap, so I'll buy those and see if it helps.

 

Thanks!

save yourself the trouble and swap the whole CPU board first, then narrow down the problem.

[RodLightning]

save yourself the trouble and swap the whole CPU board first, then narrow down the problem.

 

I agree. Best does list them as being in stock. It doesn't specify which revision they are. Having version A might simplify your incognito upgrade.

[BillC]

 

I agree. Best does list them as being in stock. It doesn't specify which revision they are. Having version A might simplify your incognito upgrade.

He has a 400 & 800 which both contain a CPU board, so he already has parts to swap for testing, he could wait to order parts once he identifies the problem.

[Joey Z]

He has a 400 & 800 which both contain a CPU board, so he already has parts to swap for testing, he could wait to order parts once he identifies the problem.

yeah, that's what I meant, don't order until you narrow it down, but start by swapping the entire CPU board to verify that the problom is somewhere on that board. also, all the LSI chips should be reseated on the CPU board itself, CPU, ANTIC, GTIA. I once had a 400 with a rolling screen problem. I opened it up, pulled the CPU board (and the RAM) and plugged it back in. no more problems after that.

[55five66six]

 

I agree. Best does list them as being in stock. It doesn't specify which revision they are. Having version A might simplify your incognito upgrade.

 

Unfortunately, after cracking my Atari 400 open, it looks like I have a REVD CPU card in there as well.

 

I will say that cracking these Atari systems open makes one appreciate the ingenuity that the engineers used to create these units.

 

I'll replace the CPU board first and see where that gets me.

 

I'll write back soon!

Edited September 15, 2013 by SoilentGreen

[55five66six]

yeah, that's what I meant, don't order until you narrow it down, but start by swapping the entire CPU board to verify that the problom is somewhere on that board. also, all the LSI chips should be reseated on the CPU board itself, CPU, ANTIC, GTIA. I once had a 400 with a rolling screen problem. I opened it up, pulled the CPU board (and the RAM) and plugged it back in. no more problems after that.

 

I swapped the CPU cards. This worked. So, It seems my problem is there.

 

Would it be worth my time to troubleshoot to which chip is doing causing the problem? Or would I be better off just buying a new CPU board?