Over clocked atari vcs cpu board

[klokwrkblu]

By means of removing the 1 mhz 6502 cpu with one 20 mhz and then clocking all the other components,

 

Is it even REMOTLEY possible to make an atari 2600 run 20 times than it was designed for?

 

Or is this just the pipe dream of an atari dunce?

[supercat]

Is it even REMOTLEY possible to make an atari 2600 run 20 times than it was designed for?

 

What would you be trying to accomplish? The CPU speed is tied in directly with the display refresh. It would be possible to add an interface to allow the CPU to run at a faster speed except when interfacing with the TIA or I/O (to be useful, the interface would have to include 128 bytes of fast RAM to use in place of the RAM in the RIOT). But what would be the point?

[Math You]

The CPU speed is tied in directly with the display refresh.

Just out of curiosity, would a CPU running at twice the normal speed give you twice the horizontal resolution? Edited October 26, 2008 by Math You

[supercat]

The CPU speed is tied in directly with the display refresh.

Just out of curiosity, would a CPU running at twice the normal speed give you twice the horizontal resolution?

 

Televisions require the horizontal sync to run at 15.75Khz +/- 1%, and require the chroma clock to be 3.579545Mhz +/- 0.05%. The TIA dot rate is fixed equal to the chroma clock, and horizontal sync is fixed at chroma/228.

[MiKOTRON]

Yeah, sorry Clockwork Smurf. It just won't jive.

[mos6507]

Years ago I think someone on Stellalist actually managed to double the clock speed and got a picture out where it was just scrunched to the left. Try searching through the archives.

[Ben_Larson]

Years ago I think someone on Stellalist actually managed to double the clock speed and got a picture out where it was just scrunched to the left. Try searching through the archives.

Yea someone did it about 10 years ago I think. Not sure what the results are but I remember seeing it in the archives.

Televisions require the horizontal sync to run at 15.75Khz +/- 1%, and require the chroma clock to be 3.579545Mhz +/- 0.05%. The TIA dot rate is fixed equal to the chroma clock, and horizontal sync is fixed at chroma/228.

I'm not sure about how exactly the horizontal sync timing occurs, but IF it's tied to the color clock and IF you could change the color clock multiplier then I guess theoretically you could overclock the CPU and also get a stable picture...i.e. CPU at 3.58MHz with 1x color clock multiplier. Although it would probably be somehwat useless seeing as everything would be restricted to the left 1/3rd of the screen i think.

 

Ben

Edited October 27, 2008 by Ben_Larson

[cwilkson]

That somebody was me. I don't remember the details but it was nasty. I doubled the clock rate of the system I think. I do remember that I had to take only everyother sync pulse. I think I used a T-flipflop to divide the frequency and ANDed that with the double-rate sync. That wasn't quite right so I started branching out from there. It took a while to find a TIA that could handle the higher speed. I think the 6507 was easier. Or maybe I used a 6502? And I was working blind...I had to watch the video waveform on a scope to find chips that could work before I could try to stabilize the picture. I do remember plugging Combat in and it was displaying a 2x2 grid with all the H- and V-blanks included. So if you had 2 frames (a and b) with 4 lines each normally, the "super" display looked something like this:

----------------------
--a1a1a1a1--a2a2a2a2--
--a3a3a3a3--a4a4a4a4--
----------------------
----------------------
--b1b1b1b1--b2b2b2b2--
--b3b3b3b3--b4b4b4b4--
----------------------

It looked kinda weird but I image it could have been made use of for something. But not in anything like a mass produced way - it was really hard to make it work. If you want to try over clocking in a useful way, I'd say separating the 2 chips into separate clock domains as someone else suggested would be better. Leave the TIA at its native frequency and try to muliply the cpu clock. And of course replace the 6507 with something that can handle higher frequencies. And probably the RIOT. You need that fast RAM. But then this is starting to sound a lot like Chimera....

[Chris Strong]

That somebody was me. I don't remember the details but it was nasty.

 

Wow. I can't imagine wanting to bother.

 

From what IC did your avatar come? I've not seen it before. I assume an ST part.

[cwilkson]

Seemed like a good idea at the time.

 

My avatar is a photograph that I took of the TIA die. The white text is the top (only) metal layer. The blue background is glass over the silicon substrate.

[mos6507]

Leave the TIA at its native frequency and try to muliply the cpu clock. And of course replace the 6507 with something that can handle higher frequencies. And probably the RIOT. You need that fast RAM. But then this is starting to sound a lot like Chimera....

 

That's why I'm more for just maxing out the capabilities of the original hardware without cracking open the case. An enhanced TIA mode would be a nice bonus For a Flashback 2 portable, though, since you could write games exclusively for it. I suspect such games would look very similar to Atari 8-bit titles, however.

[Ben_Larson]

That's why I'm more for just maxing out the capabilities of the original hardware without cracking open the case. An enhanced TIA mode would be a nice bonus For a Flashback 2 portable, though, since you could write games exclusively for it. I suspect such games would look very similar to Atari 8-bit titles, however.

Yea if the goal is to get higher resolution, then there's other more practical alternatives to experiment with. I remember someone else on the stellalist a while back managed to get the VCS to generate an actual 525 line interlaced NTSC signal as opposed to the usual 262.5 line one, effectively doubling the vertical resolution. Don't know what came of it though, except for a simple demo. Then there's the color-switching technique roland P is using with the ballblazer demo which sort of gives a 53.3-pixel wide 'playfield' instead of 40 pixels wide. To my knowledge I don't think anyone has used such a technique before, in an actual game at least...

 

Ben

Edited October 28, 2008 by Ben_Larson