DIY eprom cartridge ?

[Yoruk]

Hello there,

 

Quick question... I have a 7800 but didn't have a lot of games. For my 2600 I created a simple PCB with ROM chips inside (UVPROMs actually) that allow me to flash any game on it and play it on the real machine. I also slowly learning 2600 programming, so I'll use this board to run my own creations. ?

 

So my question is can I do something similar with the 7800 ? There is a lot (too much ?) schematics variations available online, like these ones :

 

http://atarihq.com/danb/7800cart/a7800cart.shtml

 

If I choose to make one, is there an "universal" simplest design that I should follow ?

 

And they say here about game locking authentication that "This led Atari to incorporate authentication features in its later console, the Atari 7800, to prevent other companies from creating and selling their own 7800 games without Atari's permission." So it's actually impossible/hard to play homebrew creations on the physical machine ?

 

As you can see I'm a bit confused, so any thoughts on this are welcome !

[+slx]

Code for US 7800s needs to be signed, see here for a tool/code to do that. Don't know about the hardware. 

[Yoruk]

Thanks, I was afraid that some special hardware was needed to avoid this problem. If it's only dealing with code it's quite easier.

 

I'm not ready yet to run my own programs, but I'll keep this code tool in my devs folder !

[Yoruk]

I'll try to answer...

 

So the 7800 memory map says that the ROM is 4000 - FFFF, so 48 kB in total.

 

The only 48k schematics is this one : http://atarihq.com/danb/7800cart/C026445.shtml

It uses a 32k ($8000-$FFFF) and a 16k chip ($4000-$7FFF).

 

But there where a lot of 32k designs, like this one, described as the "standard 7800 cart" : http://atarihq.com/danb/7800cart/C024926.shtml (32k between $8000 and $FFFF)

 

What is the "average" game size for the 7800 ? I know that is was 4k for the 2600, but it looks like 32 could be enough for a majority of games...

 

Maybe it's better to build the first version, and put only the 32k chip for "small" games ?

[ongikong]

Here you can find a schematic for a 48K eprom cartridge:

for a 32K eprom cart you can watch this video and read its description:

 

[Yoruk]

Thanks @ongikong

 

I'll dig into this. Regarding the video it looks like the adaptation simply consists into a pin by pin rom replacement (by a 27c256) BUT I need to invert the /OE signal. Looks like the original atari ROMs OE signal is active high, not low.

 

Didn't have my 7800 right now with me, but I'm sure that's a PAL version. I learned in your post that most of the PAL games versions are 48k, so my I'll try to adapt the C026445 version with both standard EPROMS. I'll draw a PCB, as I don't have spare carts to use... (And honestly the result presented in the video is a bit... ugly)

 

Did you manage to build other pcbs than the 128k version + RAM ?

[ongikong]

Hi! I built myself three types of 7800 eprom cartridges:

32K, 48K and 128K (with socketed ram). With those I can run almost the complete library and homebrews.

 

Please take a look here for Trebors awesome game rom collection.

https://atariage.com/forums/topic/260584-trebors-7800-rom-propack/?do=findComment&comment=4340675

 

After downloading the zip file you can obtain a nice overview of the different game sizes

[Yoruk]

Thanks ! I'll dig into this.  ?

 

By any chances, have you written down some schematics for these cartridges ?

 

Looks like that I can re-use the original Atari design, but with adding an inverter for the /OE pins... But if you can confirm...

Edited April 20, 2020 by Yoruk
grammar

[Trebor]

2 hours ago, Yoruk said:

By any chances, have you written down some schematics for these cartridges ?

Each of the cartridge types listed in the below link, provides another link for the respective schematic:

 

https://atarihq.com/danb/7800cart/a7800cart.shtml#types

 

Thanks to Dan Boris!

 

*EDIT: My bad; you're referring to schematics to these 7800 eprom cartridges from @ongikong

[Yoruk]

I saw these schematics, but I'm a bit confused about the memory chips. No chip reference are given, and it looks like (as presented in the video from the first post of ongikong)

that we need to invert the /OE signal from the machine if we use "classical" memory ICs like a 27256. This is what I wanted to confirm...

[ongikong]

Yes. You can simply solder in 2 jumper wires to use a standard 27C010 EPROM in a 128K cartridge.

If you have a 27C1000 you can replace it 1:1.

 

 

Please read also this post and further:

 

 

[Yoruk]

Thanks !

 

Here is the result of the modifications made in the video :

 

 

Nothing complicated.. To use a 27256 eprom, we just have to invert the /OE signal taken from A15.

 

Now for the bigger capacity presented (27C010 eprom) I need to understand why an inverter isn't necessary...!

Edited April 23, 2020 by Yoruk
issue with image