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Crossbow take me by the hand and sit me down

Cousin Vinnie

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Well Vinnie modding the 7800 to play Pal games isn't all that difficult. But you have to be willing to take a soldering iron to the 7800 itself. The ease of doing it really depends on the model you have. For me it was a quick 5 min thing. All the ICs in my 7800 are already in sockets (84 models are this way...). So all I really had to do was to replace the bios rom with a new modified one that goes around the encyption hence allowing me to play the pal carts. The particular chip I have is also the one from Eckhard's dev kit so I also am presented with a menu when I first power on my 7800 that allows me to dump the cart to the pc, play a 7800 game, or a 2600 game.


While I can play pal carts in theory. I haven't actually tested the real compatibility of it. Apparently there are other issues besides the encryption check. I have heard reports of some games simply not working or getting corrupted graphics. Also I don't know that the colors would be right (probably not). And of course you have to have a TV that can handle it.


The biggest pain in the modding process at least for me, was actually getting the new eprom burned. I had access to the chips but not a burner. So as luck had it...3 months after starting this and looking around, one of my students in class said he could burn the chip no problem. I gave him the docs from Eckhard's kit with the instructions on how to burn the eprom itself and gave him the file containing the new BIN to burn in it. 2 weeks later I received a package in the mail with my new bios rom.


All I had to do was complete the mod by cutting a trace on the underside, pop in the chip, move a jumper, and finally take a garbage bag tie and use it to reroute the newly cut trace back to a newly piggybacked SL704 Sram on the front side.


I have pics of both the front and back of my modded 7800 if anybody is interested. But you have probably seen them before.




The mod difficulty really depends on which eprom you use, and the model of your 7800.

Since the later 7800s didn't have the sockets for the ICs you have to unsolder the bios rom from the board and then replace it with a 28 pin socket from which to stick it back in place with.


I really think that Mitch or Eckhard would be best to ask this of. But I bet I could mod just about any model given Eckhard's instructions. I am not sure on the Pal models though. I do know that just about all the Pal units have socketed ICs in them as well. And according to Eckhard are actually much easier to mod than the NTSC units are.


You know...thinking about this it makes me realize that Atari was the pioneer again. The 7800 would be about the first console if you go from a completed design date point that had a region lock out technique on it. And would also make it the oldest console to require a "Mod" chip so to speak...heheh...who knew?


Now Vinnie, as to your question regarding the programming aspects of the 7800. Here is where things get a tad on the trickier side. The 7800 unlike the 5200 or the other 8 bit line didn't actually use sprite or title rendering processes to produce the graphics. The 7800 is a scanline renderer just like the 2600 was/is. So video tricks had to be implemented to achieve some of the graphics that were done. Also the 7800 has a limit of accessing only 32k for a cart. So once again bankswitching routines had to be used to get the larger carts done. Part of the hurdle of 7800 emulation and new development lay in the lack of documentation regarding how the Maria handled the graphics. Now that Curt has 'Creatively Aquired' this information from GCC the encyption scheme can finally be programmed around and the video tricks that some of the games used can be more easily replicated.


At least...I hope this is how it becomes. The 7800 uses basically the same processor that the 2600 uses only it is modified in the fact that it can halt the instructions on the fly. Also the 7800 in the 7800 mode runs a tad faster than the 2600 does. Otherwise what really makes the 7800 a 7800 is the Maria graphics powerhouse hiding under the hood. (Damn good chip for its day).


I regret that I can't really give anything more specific than that Vinnie simply because I myself am not a programmer nor do I really know how to code myself. Perhaps someday I will learn these intricasies (SIC) and actually be able to contribute more than just my 2 cents on reviewing games.

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