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Branching Out

Posted by atari2600land, 07 December 2017 · 200 views

So for all of yesterday and today I have been working on a 2600 project which is frustrating the crap out of me. I hope to make this into a game that I can actually play and stuff but for now, I've been laying the foundation for it. While I'm wondering if I can do it in 2k, I think that I can definitely do it in 4k, and I should probably learn how to do a 4k game in 2600 assembly anyway. The hard part has been making the scanline count steady at 262. I've also been using the branch guide located in a previous project's thread topic that someone posted there.
I am also wondering what the actual difference between a 2k Atari 2600 game and a 4k Atari 2600 game is (besides size, of course). Do they use different chips or something? If not, why didn't Atari know from the start they could use 4k on a 2k chip?
So I went to sleep at about noon. I wanted to earlier, but I had to go to the store at 11am. So I acted really sleepy at the grocery store. I got food, came home and slept. I woke up at 8:30pm. I guess I changed my life around again so I'm sleeping in the daytime and am awake at night. While I'm typing this, the title theme from BMX AirMaster for the 2600 is playing. I tested my game earlier when I got the scanline count issue under control. But I doubt it will stay that way once I introduce players 1 and 0 and missile 0. All part of the "fun" of programming, right?

I haven't checked the actual ROM chips used in Atari 2600 games, but a 2316 ROM or possibly 2516/2716 EPROM holds 2 kilobytes of data while a 2332 ROM or a 2532 or 2732 EPROM (different pinouts) holds 4 kilobytes of data. So yes, those are different chips. It is also possible that Atari used two 2316 ROM chips instead of just one 2332 chip, and the circuit board "glues" them together. Larger than so I understand bank switching is required.

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