Vigo

Could somebody confirm that the main crystal is 14.31818Mhz?

Hi, does anyone know how fast the main oscillator on the PONG arcade PCB is?

Since the Atari 7800 has a 320x200x2 display mode, a 1:1 arcade conversion could be made. Though this cartride would need 16K extra ram to store the bitmapped gfx display.

It would be really cool finally showing what the MARIA chip can finally do..... Sadly i have the skills, a little bit of interest, but absolutely no time to do anything in this direction (first i gotta make a devcart...)

You gotta be kidding! Compared to the Pokey, NES sound really kicks ass! Some tunes like "Super Spy Hunter", and most Sunsoft/Konami in-game musics could n-e-v-e-r be possible on the Pokey. Sure, you could convert the melody, so that you would recognize the tune, but it would just be small shadow compared to the original. My personal Hitlist: Best gfx: Sega Master System (although the 7800 has a VERY innovative concept of rendering the graphics - the Jaguar uses the same method. I think Maria can do much more than we see from the existing game library) Best Sound: NES (5 channels with 2 squarewaves, 1 triangle, 1 noise and 1 DPCM channel kick ass - though not as good as the C64) Best Games: NES (Yeah, sure, there are many, many bad games (THQ, Hi-tech expressions, etc...), but every system which is supported by Konami, Namco, Capcom, Nintendo, Square, Sunsoft is a winner!) Worst gfx: Atari XEGS (Sorry, as good as the chips were, by 1985 standards really outdated) Worst sound: Atari 7800 (without Pokey) (No wonder when you consider that Saturday Night Fever was running in cinemas when the soundhardware was designed) Worst games: Atari 7800 (But i really love Ballblazer, Food Fight, Ninja Golf, Ms Pacman, although these games cannot be compared to games like Zelda, SMB3 and Castlevania) All in one: i love being an 8 bit collector...

The interesting part is that when i power up without a cartridge, some patterns actually re-occur from time to time.... I already figured that out when i was a young kid...

Ok, if you ask for more.... (CLICK) But wait! I actually realized that there can´t be a winner, since every old architecture has its advantages and disadvantages. And i like both machines very much. But I just dont like biased comments like "Huh, the Coleco cannot hold a candle to the 5200". This, honestly, is rubbish. On both consoles, games can be made which are not equally possible on the other side. And if you may ask yourself why i changed my mind, i actually didnt change it. I just really love pushing technical debates.... But as a matter of fact, Atari could have been done better than just repacking the existing 8 bit chipset into the 5200. I wonder if some of those PAL prototypes were actually found.... Regards Vigo

DING, DING! Round Three! Well, of course they look great considering these limitations. But it´s nevertheless a drawback. Small memory footprints are 1979 issue... Well, you actually CAN consider this a true bitmapped mode, since every pixel on the screen can be manipulated independently. And the Coleco version of DK isnt really good, thats true. But it could have been done much better, its one of the first games of the system. Wanna play Super Breakout? Lets do the math: Coleco: 4x16=64 sprite pixels. Atari: 5x8=40 sprite pixels. If you call this rather similar..... About the length: the thickness is important... About the Sprite multiplexing and colour changes: Yes, if you stuff your display list full of DLIs, actually some nice effects can be achieved. But this requires a great amount of CPU time, when the CPU has to write to the position/colour registers multiple times.... You forgot to mention that 16bit channels downgrades the number of voices to 2. And yes, the SN76489 has also channel-independent volume registers to emulate ADSR. The distortion modes: well, if you get the kick out of it, so be it... :wink: Nevertheless, both coleco and Atari sound crappy antique. BTW, the SN76489 is NOT related to the YM2149/AY-3-8910 Ok, i forgot to name it software scrolling. Well, Coleco has software scrolling, Atari has software sprites... Why should i? Its what the machine makes very interesting, that´s perfectly clear. Lets face it, the Atari is a powerful raster machine (Atari 2600 heritage), and the Colecos strength lies in displaying detailed Backgrounds and Sprites. With the Atari, you got a lot to play with, trying to push its limits far, the Coleco is more Arcade based, with its tile structure.

Yeah, and the Colecovision is just a reboxed TI99/4A (except the cpu).... Well, the Atari actually has a wide range of display modes, but only a few are really useful for 1982 games (in 1979, it was different). What do you wanna do with double-height characters? Atari has bitmapped display modes, so has the coleco (the 768 character mode, enough redefinable characters to fill the entire screens). ;ore powerful sprite capabilities... I wont call 4 blocky 8x8 pixel players and 4x2 bit missiles more powerful than Colecos 32 16x16 sprites.... In terms of pixels, the coleco can display more Sprite pixels per line.... MUCH better sound... Well, ok, Pokeys 8 bit frequency divider is of course better than Colecos 12 bit frequency divider, yes.... In terms of sound, both consoles are rather crappy compared to other 8 bit systems (C64, NES). Hardware scrolling... Ok, thats a point. Hardware scrolling is easier on the Atari, but can also be achieved on the Coleco (Well, Ok at the expense of CPU power). Well, its of course easy just calling the Coleco completely inferior to the 5200. The Ataris are great architectures, no one has achieved what they did in 1978/79. But the fact is, they just let time pass by, and the competition grew....

Well, the concept of display lists from the Atari chipset is really ingenious, and i also really like the number of coulours the system has... But the big advantage of the coleco really comes down when looking at the, what you call "high-rez" mode of the TMS9918. Having two independent colours each line of a 8x8 pixel block enables the coleco to display more detailed gfx than Atari´s 160x192 mode. Sure, every coleco game could be done on the Atari, but it would look in all cases less detailed. Just look at some late MSX 1 games, and you get a perfect sense how great games could have been looked if the coleco lasted longer. Btw, since GTIA, ANTIC and POKEY were not designed for the 5200, i could also call them off the shelf components....

Hi! I´m also modding my 7800, and i can verify that it seems to be "normal" to the MARIA colour output.One could solve this problem by delaying the choma signal for about 300-400 nsecs....

It depends on what one would define as success... Technologically, the 5200 recycles the Atari 8 bit chipset, which is better than the Intellivision (and the Coleco in SOME aspects), but it was already 3,5 years old. This makes the 5200 look like a really quick hack job with no real effort put in. Hmm, i´d really love to try making a PAL 5200 using my PAL Atari 800XL chips.....

Hi again. So today, i connected a 470pF capacitor between the chroma resistor and the luma output, but sadly there is no improvement. I have the feeling that the noise is due to poor engineering from Atari... Am i the only one with a PAL 7800, which managed to get some sort of coloured picture at least? What if i would replace the 4,43Mhz oscilating curcuit with a 4,43Mhz oscillator (the square, blocky ones, which dont need any extra components to ocillate)? I´m really trying to be the first PAL 7800 user to get it right...... Regards Vigo

Thanks, Mitch for the valuable advice! The schematics are also the right ones! Right now, i dont have a 470pF capacitor right there, but tomorrow, i´ll give it a shot! Well, i´m taking the croma signal from the left side of the resistor, since on the right side, it´s much too weak to get recognized.´ But right now, i dont have a S-VIDEO cable handy to try this, but i can definatively say that the noise is in the croma signal, since the luma is 99% noise free. As i said, when i´m done with this modification, i´ll post the instructions how to do it here on AtariAge. Thank you very much Vigo

Well, i´m using a variable resistor on the chroma line (1k), but no matter how far i adjust it, the waves do not disappear (they get weaker, but also the colour saturation). Hmmm, i do not use any kind of capacitor.... The problem is that all video mods are NTSC only, and the layout of the PAL 7800 differs quite a lot (not mentioning the technical differences between PAL and NTSC). Even the schematics on AtariAge do not resemble my late 1991 model. When i´m finished with this, i´m going to write it down how the modification is done....

...and here with disconnected chroma signal.

My circuit currently uses the 7800 chroma signal only. I´m directly taking it from the Maria chroma pin. Here is a grab from this modification. Note the wavy pattern in the green and the purple colours...

Hello guys! I am currently going to add a composite video output for my PAL Atari 7800 from 1991. I succeeded in re-building the luma output, which gives me a real sharp noise-free black & white picture for both MARIA and TIA video output. However, in 7800 mode, the MARIA chroma output seems to suffer from crosstalk video noise, which doesnt look quite sophisticated. I connected it directly via a resistor to the luma output. The crosstalk becomes worse when i put my finger on the 4.43Mhz colour oscillator. Has anyone any idea how to fix this? Regards Vigo