Atari 2600 - use a microcontroller instead of eprom in a cartridge?

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fakebutt
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Atari 2600 - use a microcontroller instead of eprom in a cartridge?

Postby fakebutt » Thu Jun 18, 2015 6:29 pm

Hi,

I am new to this forum. In fact I just googled "atari forum" and got this as a first result so here I am :)

I have basic programming and electronics knowledge and have an idea to use a cheap microcontroller to replace the eprom of an atari 2600 catridge.
A few years ago I played a bit with the Batari Basic and ever since I have always wanted to have a homebrew game playing on a real system.

I plan to use an attiny85 or an atmel328p (the one in the Arduino Uno) microcontroller, some shift registers for expanding the input and output and perhaps an external storage (an SD card or a cheap memory chip). The microcontroller will read the address lines and will output the corresponding data from it's memory to the data lines. I think today it's much easier to program and interface with microcontroller than an EPROM or EEPROM chip.

Please share your opinion why this won't work or what I can do to improve it.
Also is this forum the right one for such topic?

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Re: Atari 2600 - use a microcontroller instead of eprom in a cartridge?

Postby simonsunnyboy » Thu Jun 25, 2015 4:17 pm

I doubt it ill work unless the micro serving the data is a lot faster than the access rate by the 2600.
Measure the bus timings of the 2600 for all select and strobe signals first and then calculate if you can come near that with a micro.

I had the same idea years agao and never attempted it due to the likely problem of not meeting the timing requirements.
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Re: Atari 2600 - use a microcontroller instead of eprom in a cartridge?

Postby exxos » Thu Jun 25, 2015 4:27 pm

There someone about who made a cart with loads of games on it. I was going to make one, but someone else already did it. Not sure what site it was, maybe someone else here knows..
4MB STFM 1.44 FD- VELOCE+ 020 STE - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - various clutter

http://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
http://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.
http://ataristeven.exxoshost.co.uk/Steem.htm Latest Steem Emulator

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Re: Atari 2600 - use a microcontroller instead of eprom in a cartridge?

Postby yogi2015 » Fri Sep 04, 2015 1:16 am

fakebutt wrote:Hi,

I am new to this forum. In fact I just googled "atari forum" and got this as a first result so here I am :)

I have basic programming and electronics knowledge and have an idea to use a cheap microcontroller to replace the eprom of an atari 2600 catridge.
A few years ago I played a bit with the Batari Basic and ever since I have always wanted to have a homebrew game playing on a real system.

I plan to use an attiny85 or an atmel328p (the one in the Arduino Uno) microcontroller, some shift registers for expanding the input and output and perhaps an external storage (an SD card or a cheap memory chip). The microcontroller will read the address lines and will output the corresponding data from it's memory to the data lines. I think today it's much easier to program and interface with microcontroller than an EPROM or EEPROM chip.

Please share your opinion why this won't work or what I can do to improve it.
Also is this forum the right one for such topic?

Well, this has been done with the Harmony/Melody cart @AtariAge. They are ARM based and offer a SD card interface. Full respect if you are planning the project for a learning experience.
The ARM is running @ >70MHz to to have enough cycles to process the reads from the VCS. At one point I too had thoughts about a similar ATMega328/NES cart but even @ 16MHz there just wasn't enough cycles for the Mega to service the NES; but the 2A03 is running about twice as fast @ 1.79MHz. Still, the timing for the Atari buss will be tight; you will only have 1/2 of the Phi2 clock to decode the address, fetch the data and drive your data pins. Be prepared to count clock cycles and write your loop in assembly :)
One of the major problems with the VCS is the lack of R/W signal at the cart port. If you look into the banking schemas that were used, they had to jump thru hoops to effect a bank switch.
Yogi

fakebutt
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Re: Atari 2600 - use a microcontroller instead of eprom in a cartridge?

Postby fakebutt » Mon Sep 14, 2015 6:49 pm

I'm a bit late to reply but better late than never. The site was not loading for me for a few days after I posted and then I had to work on some other important stuff.

I think you are right about the timing. I've done some more thinking and research and it seems it's not going to be as simple as I was hoping it to be.
I'm also finishing university (hopefully) and moving to a different town so won't be able to use the uni equipment and it will be next to impossible to attempt it without an oscilloscope. Maybe I'll find a hackerspace after I move and try it.

Thank you all for the replies!


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