-=Lindsey=-

The cost is a bit of a concern. Obviously the cost will be more than a basic cart with an EPROM and a 16V8 but how much more is yet to be seen. The raw cost shouldn't be more than a few bucks more but they will take a lot longer to assemble. So... what would be an acceptable cost for a finished cart PCB? Obviously lower is better but how high is too high?

Agreed on all counts. Seems like the most important things are emulator support and ease of programming. I think the first step is going to be creating a prototype cart and writing the C code to make it work. That should take a couple months

Unfortunately I don't have any for sale right now. I'm still deciding on the final bank switching scheme and I'm going to add RAM. The design I've got now is basically just a 32K cart and I would like to up the RAM and ROM.

It really depends on what you want to do and what kind of game you want to write, but in many cases you're right. Obviously 1K has been enough to develop 99% of all the great games that currently exist for the system. That's debatable. Additional RAM could definitely be beneficial for new homebrew titles. But again, depending on what kind of game you want to write and if you can make use of more RAM in that code. If all the cool MSX games use more than 1K it stands to reason that the ColecoVision could benefit from more than 1K. The question of whether 24K is enough has obviously been answered Do people writing in assembly tend to have more RAM limitation problems than people writing in C? That seems counter intuitive. Maybe people writing in C tend to write less complicated games? Why is that? Is it a RAM or ROM limitation? Recursive functions, tons of global variables, etc... It's really up to the programmer but my original question is starting to seem a little ridiculous because 24K is obviously WAY more than enough. Adding RAM to the console shouldn't make development much more difficult. If anything it will make it easier in some ways. You're right though, more complicated games will definitely take more time to develop. You could make an infinite number of games with virtually no RAM at all too. Well... I guess you would need the VRAM Agreed. I still think it would be cool to expand the horizons of the system and keep the cost reasonable enough that it can make the whole thing more fun for the developer and player. With 32K SRAMs under $2 it just makes sense to add RAM to the ColecoVision. What you've made me realize is that a dedicated piece of hardware connected to the expansion port to add that RAM is probably not the best approach. RAM bank switched and added to the cartridge address space is more painful to access in software but ultimately the best overall approach. You're right in that any expansion is going to need games written for it to be useful and an adapter connecting to the expansion port limits the market to only people with that expansion. The solution is definitely in the cartridge connector. I just got distracted by that damn expansion connector because it's so clean and easy to access the logic I guess I should have asked BEFORE designing the board. hehe

I've been kicking around some hardware ideas lately to add RAM to the ColecoVision via the expansion connector. There is a nice chunk in the memory map from $2000 to $7FFF. Adding RAM in that are would be pretty easy, giving a total of 24K of RAM and leaving the cartridge port space ($8000-$FFFF) untouched. Then I started thinking about bank switching the RAM to add even more but this would add considerable complexity to the design, by comparison. In short, it's the difference between using a GAL22V10 for the logic and having to move up to a 44 pin CPLD. I could accomplish the RAM bank switching with just the 22V10 but I would also like to add ROM to the board to replace the original BIOS and there are not enough I/O pins on the 22V10 to do both (Bank switched RAM and BIOS ROM) and still have byte-level address decoding. So my question to the homebrew coders is: How much RAM is enough? Is it worth the extra hardware cost and complexity to bank switch the RAM or is 24K enough?

The RAM will be in the cartridge but the access to the RAM will be different compared to RAM connected to the expansion port, in terms of programming. There will be an extra step involved in reading and writing to the RAM based on having to pre-set the R/W signal going to the RAM by a read/write to a specific address. RAM connected to the expansion port wouldn't require this step. If your program requires a huge chunk of RAM where you'll be doing a bunch of reads at a time or a bunch of writes at a time it will be pretty fast. If you're doing a bunch of individual reads and writes and you need the fastest possible performance it could become a problem. The concept should be similar to using the VRAM. Emulator support shouldn't be difficult. There are a few open source ColecoVision emulators out there. My first approach would be to have the original author mod the code but I could put something together based on an open source emulator if I had to. What ColecoVision emulator are most people using for development? EDIT: Forgot to answer this one. Bank switching and programmatically setting the RAM R/W inside the cart shouldn't be a problem in C but I don't have experience programming for the ColecoVision so someone feel free to chime in if I'm wrong. The most likely scenario would be inline assembly in the C code to read/write to the bank switch addresses but again, I don't have Colecovision programming experience so it might be just as easy to do it in C with an existing module.

Thanks for the link. I read a little about that project and it looks really cool. Should be a nice product when finished. I first looked at the ColecoVision schematic only a few days ago and started designing hardware for it but I've done a lot of design for 8-bit computing systems in the past. Looking at the schematic, that expansion connector is a really attractive place to add hardware. With that port you've got access to all of the signals you'll need to do anything you can dream of with the Colecovision. The biggest advantage in terms of adding RAM is access to the CPU R/W signal. The more I think about it the more I lean toward developing something using the expansion connector but right now I'm working on something for the cart connector. The down side of developing for the expansion connector is that huge edge connector and increased PCB size. Basically, it costs more. With FPGA and the ColecoVision expansion connector the options are pretty limitless.

I had an idea about adding RAM to the ColecoVision via the cartridge slot for homebrew game development. This method might even already be in use but I wanted to get some thoughts on it. Basically, we would add an SRAM and byte-level address decoding to the cartridge. Then we can define an address in memory that will let us toggle reading or writing to the RAM the same way you would switch banks in a typical bank switching scheme but instead you're switching between "read mode" and "write mode" for the RAM. This is a work-around to the CPU R/W signal not being present at the cartridge connector. Obviously the usefulness of this RAM is going to be dependent on the program but would this be useful?

Unfortunately, I think that's impossible using only the cartridge port and original game code. It should be possible using the expansion port but it would be a complicated design requiring FPGA (IMO) and at that point it makes sense to just put the whole CV in FPGA and do your save states that way (Again, IMO).

Similar... but cheaper with way less features

I don't own one but their carts look awesome. What I've got in mind could be considered more of a development tool than an every day gaming kind of tool. Nothing fancy, just the ability to dump code on to the cart via USB.

Do you happen to know what style of case retroillucid will be producing? That's an important consideration for future PCB designs.

Not exactly. I've been hacking on pinball and arcade hardware for years and recently I've turned my attention to console systems. I would like to try my hand at game coding in the future but what I've done first is design a 32K Colecovision cartridge PCB using Flash EEPROM for the ROM with a microcontroller to program the EEPROM. Basically it's a one-game-at-a-time, USB programmable 32K cart. Guess I should put some bank switching options in there too... I thought about selling some but if I do I'll probably just sell the assembled PCBs and let the buyer supply the case until the new cases become available.

Thanks! I will keep that in mind. I was reading about that. Some crazy cost involved in having the mold made. I wonder what the market demand will be for new cart cases. It would be nice if there were enough demand to get the cost per case down.

Hi All, N00b poster here with a question Is there a good source for empty Colecovision cartridge cases? Other that using old carts? I'm looking for about 100 cases. Thanks in advance.