Schematics of Dragon Cartridges?

Hardware Hacking, Programming and Game Solutions/Cheats
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Rolo
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Schematics of Dragon Cartridges?

Post by Rolo »

Hi.
Does anybody have schematics of a Dragon cartridge PCB? Or photos with desoldered parts, where one can see all the connections? What's beneath the 74LS00? :?:
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Rolo
Rink
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Re: Schematics of Dragon Cartridges?

Post by Rink »

No... but I have some home-built ones that just need final tests... so what's up?
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Rolo
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Re: Schematics of Dragon Cartridges?

Post by Rolo »

Hi Rink,
well I wanted to play around with it, try to make a cartridge, maybe a simple multicart with a bigger EPROM, if I find the time. So a sample cartridge or PCB would be appreciated.
Rink
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Re: Schematics of Dragon Cartridges?

Post by Rink »

From what I could tell from the few actual Dragon cartridges I have, most have multiple ROM chips necessitating a more complicated design than you need now.

I don't have a schematic handy for mine (will find one though) but I use a single 8Kx8 28 series flash EEPROM which means you can basically get away with taking signals from the Dragon's nicely designed cartridge socket and connecting them to the EEPROM. The only other chip I have on the board is a NAND gate to invert the R/W signal to generate a low when reading.

I have then have two jumpers - one connects Q or E (can't remember which) to the cartridge connector for autostart; the other optionally connects up the write signal. However, writing to the EPROMs from the Dragon does not seem to be working - not sure at this point whether the rom is too slow (need to try with SRAM but I don't have any right now) or whether I've made a mistake somewhere.

The most annoying problem, which I also ran in to when I build some Dragon cartridge breakout boards for experimenting, is that the D32 has an annoyingly designed connector/slot so that without putting the boards in a cartridge case, it's very easy for the signals not to make a good connection. So I built my last boards to the size of the one in Dragon chess... Which works, but makes the PCBs large and quite expensive.

Fun project though. I've little use for being able to make my own Dragon carts but it was just something I wanted to do - and a bit of a spin off from another on-going project.

A large multicart would be cool - and shouldn't be overly horrible to build.
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rolfmichelsen
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Re: Schematics of Dragon Cartridges?

Post by rolfmichelsen »

Rink wrote:However, writing to the EPROMs from the Dragon does not seem to be working - not sure at this point whether the rom is too slow (need to try with SRAM but I don't have any right now) or whether I've made a mistake somewhere.
You will not be able to write to an EPROM in that way. The EPROMs need a higher programming voltage and signal timings that the Dragon does not provide. You need a proper EPROM programmer to do that. You should be able to write to SRAM connected to the cartridge port.

-- Rolf
Rink
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Re: Schematics of Dragon Cartridges?

Post by Rink »

rolfmichelsen wrote:You will not be able to write to an EPROM in that way. The EPROMs need a higher programming voltage and signal timings that the Dragon does not provide. You need a proper EPROM programmer to do that. You should be able to write to SRAM connected to the cartridge port.
There's no voltage problem - the 28series flash roms are amazing and I use them in everything. No programming voltage needed, they generally work just like SRAMs but with slower write times.

I usually program them with a Picaxe connected through its programming cable with a hastily programmed .net tool on the PC end. Never bothered buying a proper programmer because these EEPROMs are just so easy to deal with.
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Rolo
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Re: Schematics of Dragon Cartridges?

Post by Rolo »

Wow, thank you for the response. Seems to be an interesting issue :) Strange enough, on other platforms you can find a variety of cartridges. For the Dragon I could not find any. And the machine was quite popular in England, wasn't it?
Concerning the PCB. I found an old and unused ISA-formfactor experimental PCB in the basement. I did modify it with as saw, so that it seems to fit well into the cartridge port. Maybe I'll have to sustain it with kind of housing feet or something. That should be fine for a few experiments. Again, I do not have any plans for a semi professional production of cartridges (I don't even know, if that would be legally possible.). It's just out of curiosity. Just to see, if i can make it work. And probably it will take forever, until I really find the time. For a multi-cart, i'd just take a simple straight forward design with a (DIP-switch) bank-switched EEPROM, like John Dondzilla's Odyssey 2 multi-cart.
But if anybody already has done so, I'm happy to read, what I have to consider and maybe be able not to repeat all the mistakes, that already have been made.So, thank you everybody!!!

PS: Another idea, that would even be nicer, would be to disassemble cassette tape games, more or less automatically analyze the code, change absolute addresses, if necessary and relocate it to the D32-cartdidge address-range, so that those programs could be on cartridges too. But I still don't know the Dragon well enough to judge, if that would be possible at all or if that is complete nonsense. What's the maximum address-range for cartridges? And what's the size of the average cassette game? And maybe that has also been done before (maybe by some CoCo guy)?
zephyr
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Re: Schematics of Dragon Cartridges?

Post by zephyr »

Rolo wrote: PS: Another idea, that would even be nicer, would be to disassemble cassette tape games, more or less automatically analyze the code, change absolute addresses, if necessary and relocate it to the D32-cartdidge address-range, so that those programs could be on cartridges too. But I still don't know the Dragon well enough to judge, if that would be possible at all or if that is complete nonsense. What's the maximum address-range for cartridges? And what's the size of the average cassette game? And maybe that has also been done before (maybe by some CoCo guy)?
It is possible for the few Dragon games which are small enough to fit in the 16K (-256 bytes I/O) cartridge ROM address space; but I have always found it to be a very long, boring and unrewarding task (most people don't even bother to post a thank you). I wouldn't be prepared to convert cassette to cartridge (or the other way round) on a regular basis! :)
Rink
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Re: Schematics of Dragon Cartridges?

Post by Rink »

Rolo wrote:Wow, thank you for the response. Seems to be an interesting issue :) Strange enough, on other platforms you can find a variety of cartridges. For the Dragon I could not find any. And the machine was quite popular in England, wasn't it?
Yep. I think the main part of the problem concerning carts was that comparatively few games were released on cartridges for the Dragon here. Tapes were preferred for some reason. Even the MSX, which enjoyed a huge number of cartridge-based games around the world, seems to have had most of its titles released on tape here.
Concerning the PCB. I found an old and unused ISA-formfactor experimental PCB in the basement. I did modify it with as saw, so that it seems to fit well into the cartridge port. Maybe I'll have to sustain it with kind of housing feet or something. That should be fine for a few experiments. Again, I do not have any plans for a semi professional production of cartridges (I don't even know, if that would be legally possible.).
The first breakout board I did seemed to just about work without supports but then I changed to use an attached cable which pulled down on the board just enough to stop some connections working. In retrospect, I should have made my boards fit TRS-80 cartridge cases instead, which would have been a bit smaller.
PS: Another idea, that would even be nicer, would be to disassemble cassette tape games, more or less automatically analyze the code, change absolute addresses, if necessary and relocate it to the D32-cartdidge address-range, so that those programs could be on cartridges too. But I still don't know the Dragon well enough to judge, if that would be possible at all or if that is complete nonsense.
Seems possible enough to me - but maybe not worth the work - doing it on the fly using the Dragon's CPU might be a little slow. People seem relatively happy with loading tape games from MP3 players / phones etc. One thing I did consider was using a cartridge with either an auto-start menu or an extension to BASIC to load .cas files stored on the cart into the areas of memory specified in the .cas header - it'd be like loading from tape but a lot faster. I don't know how some of the preloaders (like Manic Miner) etc. would respond since I never tried it.

The other thing to consider would be how the DOS carts work and whether their techniques could be used. I don't know much about them though.

On a related note: is everyone here using a floppy disk emulator or loading from a music player? I never saw an sdcard based cartridge for the Dragon before either.
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robcfg
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Re: Schematics of Dragon Cartridges?

Post by robcfg »

We have a PCB scan of a standard Dragon Data game cartridge here.

I don't know if that's what you're looking for or if you need more detailed information.

All cartridges I've seen are like that one.
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