Re: [stella] Over-clocking the 2600

Subject: Re: [stella] Over-clocking the 2600
From: danboris@xxxxxxxxxxxxxxxx (Dan Boris)
Date: Tue, 9 Sep 1997 08:07:36 -0400
> I heard that the TIA chip can be fed at 1.79mhz and that by doing so you
> allow higher playfield resolution and possibly other benefits.  Supposedly
> the TIA chip itself runs at 1.79mhz.
I would be interested to see if this would work. I would think that if you increased the clock rate to the TIA it would through off the video timing so you would end up with shorter times between HSYNCs and this would mess up the screen, someone please correct me if I am wrong about this.

I also assume that if you overclocked the 2600 it would mess up the timing so that existing games would not run properly on it.

> It might be interesting to see if 2600 mode can be enabled on an Atari
> 7800 without the 6502C dropping to 1.19mhz, let alone maintaining access
> to the fast 4K internal RAM.  It might then open up a whole new category
> of "2600+" games.

I have been studying the 7800 programmers guide and schematics and I don't think this will be possible. The 2600 mode is enabled by writing to a latch than then sets a signal going to the main chip on the 7800 (MARIA?). This chip takes care of generating all the clock and chip enables to switch from 7800 mode to 2600. Once this latch is set it is electronically locked in and cannot be change back without power down the system. 

							Dan Boris

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