I fixed the mistakes I made on the previous prototype, and I managed to add a small feature : it is now possible with the help of a jumper to choose between color mode, or green-and-black monochrome mode, for those who (like me) had a monochrome display, and prefer to use this mode which provides a crisper picture.

Here is a picture of the final PCB, assembled.



I still need to tweak the CPLD code a bit, but it should be now only a matter of weeks until first boards are available for those who might be interested. I'll tell more about it later.

The Chat-Mauve-clone-but-with-VGA-output needed a name, and here it is : "Guimauve 2ooo".
Here are some pictures of the first prototype, which works fine !





You may wonder what happened to what should have been a nice board ? ;) Well, I made two stupid mistakes so I add to cope with them :

• The part I selected in Eagle as the DB-15 connector on the Apple side had its pin numbering "reversed".
  
• I totally "forgot" that one of the components expected a 5V power supply, while all the others use 3.3V, so I added it.
  
  

I will have to redesign the board but well, it won't be much of a big deal.

I just finished designing the board, using parts I already own for the most :



It has been designed to be the more "homebrew-compliant" possible : it is single-sided, and there will be only a single wire to add. Next step, order parts, and build the PCB (or have it manufactured), then hope the whole thing will work ;)

Here is a new picture, with VGA colors fixed. I still use a 2-bits R-2R ladder for output, so the colors are still a bit different from what's produced by the original adapter, but I can't say that the result is better or worse, so I'll probably keep it this way.
On the left, the original adapter's output on a LCD TV, on the right, VGA output of my adapter.



The image isn't very crisp (I get a better image using Starter Board's own VGA output, even if it only features 1 bit per component). It means that it's now the time to make a proper board, instead of having such a mess of wires hanging around ;)
The desing still uses less than 60 macrocells, so it could fit into a XC9572XL for instance, which is probably what I'm gonna use at the end.

I managed to modify the VGA adapter of the Apple II+ on a FPGA to meet the requirements of my previous post.
It stills runs off the FPGA but, it uses the board's SRAM instead of internal block ram. The design fits well in a XC9572 CPLD, which is quite fine.


Colors are still a bit off, but text display works nice, showing that interleaved SRAM access works. Now I need to fix the colors (shouldn't be much of a big deal, as I already solved the issue on the SCART version), then use a CPLD, to be as close as possible of what would become a final version ;)

My "Chat Mauve" video adapter clone is now working, at least for a basic rendering.
Let's start with a picture of my mess :



On the main TV you can see it running. On the secondary TV, you can see the monochrome NTSC output provided by the Apple //c.
My design is currently running on the FPGA board, but is simple enough to run off a small CPLD. I just wanted to keep all my logic analyzer stuff in place to do some tweaking. For now, I just use a 2-bit R/2R ladder for each R,G,B output, and the screen rendering displays an horizontal resolution of 140 (instead of 280 for a HiRes screen), as my primary goal was to test the full range of colors available.

Here you can see a picture of the original Chat Mauve adapter rendering (displaying Little Computer People, a really nice game, let's call it the grandfather of the Sims) :



Now a picture of the same game, using my adapter :



As you can see, the colors are a bit different, and you can see the effects of the "half-resolution" screen rendering. Well, apart from the screen rendering, which can be probably easily fixed, the result is quite nice. I might test a 3-bit R/2R ladder if if want to get closer to the actual color display but it already looks nice.

Another thing that camed to my mind when I started this project was to make a VGA output, instead of a simple clone of the current adapter. During my quest for information on Internet, I found this project : Apple II+ on a FPGA.
It contains almost everything I need, as it can output video to a VGA screen. The 0.1 version of this project is pretty close to what I've found so far by analysis (and it also provides a 140 pixels wide rendering). The 1.0 version provides an interesting color-generation scheme, which looks pretty tricky to me, with my current knowledge of the Apple video generation internals.

I'm sure this project will be helpful, but for the VGA rendering, I will need to rework some parts, as :

• The 1.0 version of the VGA display uses a 28Mhz clock, instead of the 14Mhz clock provided on the video connector.
  
• It uses a dual-port internal BlockRAM, where I plan to use (whenever possible) a single port SRAM. Dual-port RAM is quite expensive, so I'd rather use standard single-port RAM (and it will make the (hopefully) upcoming board easier to route).
  
• It also relies on vertical and horizontal blank, whereas the video connector only provides composite blank.
  
  

Well, it's already a first major step for my project, but there's much more to come... Stay tuned ;)

It's been some time now since my last site update, mostly because of my lack of time...
Anyway, back to "work" with a new project : design a "Chat Mauve" video adapter clone at first, then maybe an enhanced version. The "Chat Mauve" adapter was designed to provide a RGB output on a SCART connector, for Apple //c computers. At Silicium, despite owning many Apple //c units, we've been able to find only one of those adapters so far, hence this idea of making a clone.
The adapter comes in a very small beige box. I opened it, expecting to find only a couple of passive components or simple logic chips in so few space, and I found myself quite surprised, as the box contains only a single custom chip (along with its voltage regulator) !
As expected, I didn't find anything useful on the web, so I searched for some information about the Apple //c video output and Apple II computers hardware. After some reading, it seems that making a RGB output out of the video signals provided isn't a trivial task, but doesn't seem too hard either.

Then I remembered a nice project I found on the web some time ago : the SUMP Logic Analyzer. It's an open-source FPGA-based logic analyser, with a client software in Java. It uses the Spartan-3 Starter Board as a primary target, which is fine, as I own one of those. So I decided to give it a try, as it should fit nicely for the project's purpose.

First step : put all the adapter's connector signals on a breadboard, and see which ones are used by the custom chip.



No big suprise here, almost all of them are used... Second step, set up the logic analyzer...



... and start analyzing, which is what I'm about to do now. I spent some time these last days to add a VHDL export to the SUMP Logic Analyzer Client, so I could use analyzer results as testbenchs for the upcoming design. On a side note, I'm using my Samsung NC10 "netbook" to run the logic analyzer client... Who said that netbooks are only suitable for basic tasks ? ;)

Last week-end, I attended the Toulouse Game Show, which is in my guess, the biggest geek convention close to Toulouse. You could find all kind of stuff, including (but not limited to) anime, manga, cosplay, hentai, arcade, rhythm games, import shops, star wars geeks, guest stars. It was very cool indeed. The Silicium association prepared a Famicom-related expo for the event.


See my Picasa photo album : Toulouse Game Show 2oo8

October is usually the month when Vieumikro occurs. Fewer people attended the event this year, but it was still very nice.
I brought a "minimal" amount of stuff this year : everything needed to repair our old machines, but nothing related to my projects. Here is a picture of my mess :



I managed to add a SCART RGB output to an old Videopac (Odyssey2) system, I'll write a tutorial about it later.

Here are some links about this event :
http://www.obsolete-tears.com/vieumikro-2008-dossier-120.html
http://sbm.ordinotheque.free.fr/vm2008/

Above is a picture of my 2600 Monocart. It's a "Flash cart" for the Atari 2600, featuring an ATtiny461 with a AVRUSB-based firmware. It also features a EPM3064 CPLD that will perform the various bankswitching stuff you can find on many 2600 carts.

I've called this project "Monocart" (as opposed to "Multicart"), because the memory size is only 32Kb, so don't expect to load tons of games into it ;)

I wanted to make the board as convenient as possible : all DIP and PLCC components (with the exception of a 3.3V LDO regulator), and standard programming headers available on the board itself.
I managed to have it work properly, but not as I intended at first. I planned to use a NVRAM chip, so it would have been able to emulate the additional RAM you can find on some carts. However, for some reason, the chip doesn't work as expected. I ended up using a standard EEPROM (28C64) and it went fine. So let's call it half-successful ;)

Now I need to write some kind of "bootloader", that will set up bankswitching, and maybe display a nice logo too ;) and write all the bankswitching logic you can find on 2600 carts (there are many of them, due to the limited 4KB address space of the 6507 CPU used in the 2600).

Later, I will try to figure out why it doesn't work with the NVRAM chip. I tried to use it on a Pixel Past PCB (suspecting a flaw in my own board design) and it failed too.

Yet another week-end full of videogames, junk food and drinks, with a bunch of friends (some of them even managed to be virtually here).



Meanwhile, some parcels were waiting for me at home. First, a bare PCB for my yet-to-come Atari 2600 Flashcart :




Then, a Megadrive clone I ordered from Play-Asia. This one features a cartridge connector, in addition to the set of built-in games you usually find in this kind of devices.




As you can see, the device is rather small. The bundled 6-buttons pads are OK, and it also features a PAL/NTSC switch. I still haven't played much with it, but it looks fine.

This year's Infoticaires meeting was very nice, as usual. I had no luck with my own stuff (my "generic linker" stopped working after a few hours), but there were so many things to do and people to talk with that it didn't matter anyway ;)

Click here for a video of this event.

I double-triple-checked my board, in order to sort out the issues I talked about in my previous post, but everything looked correct at the hardware level so far... krb then suggested to chat with some people in the PCE homebrew scene, and the well-known hacker Charles MacDonald explained me the weird ROM layout when it comes to games larger than 256Kb. After some attempts, I patched my flash programming software to take care of this layout, and it works !

Here you can see Bomberman '93 running fine on a SuperGrafx. Thank you Pascal and Charles for your help ;)

I recycled my "Generic USB Linker" gizmo to make a Flash cart for PC Engine consoles.
I etched a PCB having roughly the size of a HuCard, and connected it to my flash board, and it works... almost. For some reason, on the ROM I've tested, some sprites are garbage, but the reamining sprites/backgrounds are OK, music and SFX work too, as well as the game itself. Weird. Well it's enough for today, I'll have a look at these issues later ;)

Here is a picture for now (click on it to get a full-sized one).

Just a small picture of something I'm currently working on...



More on that later... For this one, I will have the PCB manufactured.