TRH9000 - The Yamaha V9990 based open-source video card for the MSX

WoW! Impressive! I love how devoted you are to this, @Crisag.

In the meantime, I worked a little bit on my own variation - it's got a little bit of a different focus, more trying to keep the image-quality as good as possible, than anything else.

Hello everybody. I know I'm a bit off lately, but I want to report on the latest developments for the TRH9000. I had some time the past week and this weekend to work on it.

I have the pleasure to say that the superimpose feature is now working on my prototype. However due to the challenges I had to make it work, and the differences in how RGB signals are exposed in the variety of MSX computers, I decided to release two versions of the board on GitHub: TRH9000 and TRH9000S

The biggest challenge I had was due to some MSX computers not exposing the YS sync signal that is required to control the superimpose feature on the V9990. There are ways to derive the required signal for the computers that don't explicitly offer it on the connector, but as some computers do that and some not, the complexity to research and find out if your computer offers the signal, change/make cables, etc is not just for the normal MSX user.

You can understand more just looking for the YS signal on multiple MSX computers exposing RGB on the wiki article [url=https://www.msx.org/wiki/RGB_(8-pin_DIN_45326)]RGB 8-pin DIN 45326 - MSX Wiki[/url]. You will see that some offer it, some not, some offer in different pins, together with other signals, etc

Then, the TRH9000 will have just one DB15 VGA/RGB 15Khz connector and will provide basically the same features of the traditional GFX9000. Important to mention that the new board is not using the Sony CXA2075 RGB encoder but a more modern Texas Instruments LMH1980 sync separator to form the RGB signal from the V9990 VDP. That change makes the board simpler and offers better video quality.

Here are a few pictures of the v0.3 prototype

The TRH9000S will feature two connectors. A DIN8 connector to receive RGB from the MSX computer connected and a DB15 VGA/RGB connector to output the resultant superimposed signal. Of course, there will be a way to allow MSX RGB passthrough or disable the MSX RGB input thus making the board behave like the conventional TRH9000.

So, there will be two versions on the GitHub moving forward.

TRH9000 Status

I just updated the repository with the v1.0 revision (first release). I’ve been using the board for the past several weeks and the video quality improved a lot from the initial prototypes, but of course it can be improved. I tried to isolate digital from analogic, separate the oscillators from the rest of the components, use shorter video traces on the board, etc but there is still room for improvement.

If you are curious to see the v0.3 prototype in action, please check this video of a bad player (me) playing Life on Earth TRH9000 - The Yamaha V9990 based open-source video card for the MSX - YouTube

Please note that the artifacts you see on the screen in some parts of the gameplay are due to the use of the board in a FPGA based MSX (I use one of those for development to avoid any damage to real vintage hardware).

In parallel to the effort to improve video quality, I’m also working to fit the board into a conventional MSX cartridge case. We have access down here in Brazil to factory quality ABS cases and I’ve been using a laser to create cardboard simulations before making improvements on the real board and order real PCBs.

Some pictures below

TRH9000S Status

My initial effort to implement the superimpose feature was using a LT1675 specialized RGB mux from Linear Technology. That chip is great, but requires +/- 5V, something we haven’t planned initially on the board (we have just +5V). That forced me to use ICL7660 to generate the right voltages, plus another LMH1980 to separate the sync signals from the RGB coming from the MSX… you can imagine the board would never fit a standard cartridge with so many ICs…

Then Doomn00b had the idea to use a SN74CBT3257 mux from TI. Well… results were the same with both, but the board is just a lot simpler with just that chip that with the collection of ICs I was using.

For the TRH9000S I have ordered the second batch of prototype PCBs to play with the signals. The video quality is also dependent on the developments made with the simpler version. I tested my prototype in an Omega MSX2 with success, but still need to see it working on my FPGA MSX (even changing the output to 15Khz I couldn’t see the superimposed image).

To fit that version into a conventional cartridge I think I’m already touching the limits of what is possible with routing in such a small work surface. ????

Well, that is it for today… I’ll keep you posted.

Experimenting with din8 in the next prototype. That is not the final version yet.

Will the artifacts on the FPGA MSX be eliminated when this is available to purchase (if that is an option)? I just have three FPGA MSXs.

My SX-1 is from Oct 2018, so, it was produced about the same time as KdL 3.6.2. Hard to say what 8bits4ever installed for MGLOCM firmware. The Zemmix FPGA and SX-2 will almost certainly have the artifact unless I change the MGLOCM firmware.