will 128KB devcarts ever exist for the 7800?

[gdement]

I discovered this site and others like it about a week ago, and I've been thinking I'd like to work on a Zelda-style game for the 7800. But I'm concerned about whether its going to be possible to put it on a cartridge.

 

For a game like this, I think the "Winter Games" and "Summer Games" carts make the best template, since they provide 128KB ROM and 16KB extra RAM. However, I would need the RAM to be battery backed. Problem is, it appears that the largest devcarts anyone has developed are 48KB. I even read a comment somewhere that nobody has ever successfully made an EEPROM (EPROM?) cart, but I don't know if that was accurate.

 

POKEY sound might not be possible. There aren't any games that had both extra RAM and a POKEY sound chip, and according to the "Bankswitching Guide" (which I assume most of you have seen) the 2 carts that have a POKEY implement it in such a way that it would interfere with the address space used by the extra RAM. Even if I could get by without extra RAM, it would still be needed to save games.

 

My main concern is ROM size. How likely is it that 128KB (or even larger) devcarts and EPROM carts might be developed in the future? I'm not a hardware expert, so I'm in no position to assess it or to push that frontier. If I ever succeed in writing a game like this I'd certainly like it to be able to be put it on cartridge. The hardware gurus have reached the 48KB level, but that being the limit without bankswitching I'm wondering if they're at an impasse. Thanks for any thoughts.

[+Mitch]

Well, the soon to be released Cuttle Cart 2 does all of that. However, the first run is already sold out.

There are DIY 7800 RAM carts that can go up to 144k but they are not battery backed up.

 

Making EPROM carts for the larger size games is not a problem.

 

Mitch

[Susuwatari]

There might be a solution to having both pokey and save game: use password saves. It may work if the game's simple enough but for large or complex game, password may be too complex or lengthy. (password to transfer from GBA's Golden Sun to GS2 can be up to 6 pages long and almost as complex as a single 2K 2600 game!)

 

How about bankswitching between pokey and RAM? Use pokey for sound during the game, switch to RAM for saving and loading games?

[Bruce Tomlin]

The way the "standard" 7800 bankswitching worked, there's no reason why it couldn't go all the way out to 4 megs (7800 Pokemon, anyone?), aside from that they never wired up more than 3 bits of the latch in a real cartridge, and ROM was still too expensive in the day. To get both RAM and POKEY working, you would need to use only half the ram, or use a PAL chip to do address decoding to cut a hole in the RAM area, but the real problem would be board real estate to have all three of ROM, RAM, and POKEY, along with decode logic, stuffed into a standard Atari cartridge. That's a 40 pin, a pair of 28 pin, and at least a 20 pin DIP. And surface-mount wouldn't be worth the cost for just one game.

 

Or you could use a CC2 (if you had ordered one), though I wouldn't bet on it currently having any bankswitch config with both RAM and POKEY, since no actual game ever used both.

[gdement]

Plus the battery as well... I'm looking at the PCB for my winter games cartridge, and it looks like it would be very crowded.

 

I've made assumptions about what I would need based on some info I looked up about the original Zelda game:

 

http://hem.passagen.se/flubba/download/zel...da_roadmap.html

 

Zelda was a 128KB ROM and had 8KB RAM in addition to the 2KB system RAM. Very little of the RAM was used for saved games, so it maybe used 9KB of RAM. Of course, I wouldn't want to just duplicate Zelda, but I'm using that cart to help estimate.

 

It sounds like I should try to see if I could fit everything in the 4KB system RAM and use passwords. Unfortunately I can't remember a single adventure game that had reasonable passwords. I had thought about using some form of compression in some of the ROM data, and decompressing it in the RAM when it was about to be used. Sounds like instead I should assume that the ROM could be 256KB or even larger if necessary and I should optimize for very small RAM usage. I see the 3 latch traces you referred to... would it just require 1 extra wire to enable 256KB addressing? If so, it sounds like 256KB ROM would be a trivial issue.

 

This is all speculative of course, it would be a bigger project than anything I've ever completed, but I wanted to understand what the cart limitations will be before I get too serious. In any case, I think I'll start coding something and see what I can learn. I'm just glad there's people out there who understand this hardware stuff.

[Susuwatari]

but the real problem would be board real estate to have all three of ROM' date=' RAM, and POKEY, along with decode logic, stuffed into a standard Atari cartridge. That's a 40 pin, a pair of 28 pin, and at least a 20 pin DIP. And surface-mount wouldn't be worth the cost for just one game.[/quote']

 

Board real estate space didn't stop Supercharger from coming out. They just built the board as big as needed and if anyone's determined enough, anyone can try to etch a custom sized 7800 board big enough to handle everything.

[Cootster]

Is there any upper limit to the cart sizes for the 2600/7800? IIRC, the 5200 is limited to either 32 or 48K due to the way it is addressed by the system, but knowing that Andrew Davie has made a 512K ROM image work on the 2600 (I think he used the CC1 to get it on the real hardware), and Homestar RPG will be the first released 64K game on a cart (Multicarts don't count), I would assume that it is only limited by what can be physically put on a PCB.

 

There weren't any 7800 carts released larger than 128K, AFAIK, because Tramiel was a cheapskate. Of course, considering that the vast majority of NES games released while the 7800 was in production were 128 or smaller, I don't think size was much of an issue.

[Blackbird]

Battery-backed RAM being an issue, one could use non-violatile RAM instead...

[Bruce Tomlin]

Battery-backed RAM being an issue' date=' one could use non-violatile RAM instead...[/quote']

 

I'm rather partial to the idea of using a 93C46 serial EEPROM for game saves. They're small, have 512 bytes of memory, need only 2 control lines, and don't need a battery. And for scavengers like me, they're easily found in old junker modems. As a bonus, I think the POKEY chip already has the I/O lines you'd need.

 

You'll still probably want regular RAM for graphics use, though.

[Susuwatari]

I don't think there are a physical limit to the size of 2600 game. Although when you get to a really large image, conventional bankswitching would start becoming inefficient and you'd need something like a coprocessor just to handle large ROM. By then, the cost would make the project impractical.

 

First, someone has to write a game that big. 64K is the biggest 2600 game available and hand coding 64K is a lot of work. That's probably 12-16,000 lines of code to go through if you have a rolling picture due to a missing cycle. (2K typically have around 500 lines)

[Susuwatari]

AA forum must hate me. this is like the 4th or 5th double post I've had to edit out.

[Cootster]

Inefficient for the usual homebrew profit model, yes . . . But Atari, while they were still making a profit, could've pulled this off.

 

Thanks for the answer, I was pretty sure that the limit was basically infinite, but not completely.

[Dav]

The real problem is the size of the cartridge. I'd really like something like a double ender. The only solution I have thought of is dipping the board in epoxy like a candle.

[Classic Pac]

Hey I had a friend back at Atari during it's heyday. What was planned for the 7800 some have actually accused me of making all of this up. But they were planning a RPG with battery back-up. If you think the 7800 wasn't capable of good graphics just look no further than Tower Toppler and the bonus round.

In fact the only thing I'm not 100% sure of was the max size of 7800 carts.

They did have plans for 2 meg games, that I'm sure of. But as you all know nothing ever came of those plans.

[Bruce Tomlin]

In fact the only thing I'm not 100% sure of was the max size of 7800 carts.

They did have plans for 2 meg games, that I'm sure of. But as you all know nothing ever came of those plans.

The biggest carts actually made were 128K (with optional 16K of RAM or 8K RAM plus Pokey), and 144K (with no extra RAM). Using a slightly modified "super cart" board, with a bigger EPROM and three more address lines brought to the bank switch latch, 1 megabyte. With an even bigger EPROM, and an 8-bit latch, 4 megabytes. Plus an extra 16K for RAM or ROM.

 

Battery RAM was a no-brainer except for the cost. In fact, Harry Dodgson's monitor cart had battery-backed RAM. (8K, I think) More interesting in modern times would be a serial EEPROM, up to 128 bytes with a 93C46, 512 bytes with a 24C02, or even bigger chips. All you need is two I/O lines.

[Viso]

I've been working on a solution to having battery-backed RAM on a cartridge. It is a memory module that connects through a controller port, and a controller can connect through it so it doesn't need a dedicated port. It has a simple flie system so multiple games can share the storage. I'm going to start work on the board for what I hope will be the finalized version of the hardware soon.

 

You can see more details on the page I made for it: http://home.hiwaay.net/~jeffj1/projects/amm/index.html

[DracIsBack]

Hey I had a friend back at Atari during it's heyday. What was planned for the 7800 some have actually accused me of making all of this up. But they were planning a RPG with battery back-up. If you think the 7800 wasn't capable of good graphics just look no further than Tower Toppler and the bonus round.

In fact the only thing I'm not 100% sure of was the max size of 7800 carts.

They did have plans for 2 meg games, that I'm sure of. But as you all know nothing ever came of those plans.

 

IIRC, didn't Mitch find a 512K (4 megabit) 7800 board that Atari never made use of?

[Bruce Tomlin]

I'm sure Atari wasn't very keen on the idea of a 512K byte cartridge. Especially since I noticed in the Devcard documentation where it says that Atari policy was that no more new games would have RAM in them. If they were too cheap to spring for some RAM, they would also be too cheap to spring for a ROM of sufficient density to have 512K on a single chip.

 

Besides, the Super Cart board only has room for a 28-pin ROM chip. I just opened a Commando cart and was surprised to see 32 holes on the board for the ROM. Which makes Commando the only production cartridge able to support 512K bytes of ROM.

[+Mitch]

Yep, Commando is the one that had the 512K board. Too bad the game wasn't 512K, probably could have fit several more levels in with that extra space.

 

Mitch

[gdement]

I just wish it had been 256KB, like the nes version was. The fact that the atari version is mysterioiusly half the size of the nes version says something about cheapness I guess.

[Bruce Tomlin]

There could be other reasons. Maybe the way the NES does graphics is less efficient for some reason. Maybe it's because they had to have that separate CHR ROM. Though with what I know about the way the 7800 stores its graphics, I'd be surprised if it was more efficient.