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

Expert (122)

11-08-2022, 04:15

@lintweaker - I checked your schematics and I see you are using the toshiba memory chips. I'm trying to fit everything in a small cartridge and I will be using the 256kx8bit Samsung KM428C256. I was trying to use the TSOP40II package but I gave up on the routing. That thing is small but too complex to route in such a small space.

I'm now using the SOJ package which seems more friendly to connect to the V9990. I also see you are using a flash pld. Is that for the selection logic? Are you doing anything special besides just enabling the V9990 when IO is requested on ports 60-6F?

On the project update side I started the routing challenge today. Things are moving, slowly but moving. Here is the current PCB.

Por sdsnatcher73

Enlighted (4322)

11-08-2022, 07:27

The position of the VGA connector this way may be a problem. When the cartridge is inserted in the slot it may partly be inside the machine. Or it won’t even be possible to insert it fully.

Por crisag

Expert (122)

14-08-2022, 15:01

You're right. Will move it to the top of the cartridge. Thanks @sdsnatcher73.

Por megatron-uk

Resident (51)

19-08-2022, 19:17

This is great news people!

Has anyone got a source for individual v9990 chips? We have just had a Powergraph Lite group buy cancelled part way through production as Technobytes was unable to source the ICs without something like a 500% markup over their previous supplier.

Buying trays of chips is probably too expensive now for bulk production so open designs like this are likely going to be the only way for people to get a card.

Por AndyPF

Supporter (8)

20-08-2022, 14:47

Hi, crisag. I am quite experienced in Kicad, so if you need any help in PCB routing, please let me know.
I'm following the repository, anyway.

Por crisag

Expert (122)

21-08-2022, 04:01

@megatron-uk - I have multiple sources for the V9990. I managed to buy 15 from one of them in US (after ask a lot) but now they only want to sell (or have) sealed boxes with 240 chips. Price is 42USD each for the seller in Japan, or 45USD for the US dealer.

If we get a lot of interest I can get a box and source units to the community. But first we need to finish the project.

By the way, today I had some time to invest on routing. I also started to prototype to validate the circuit as my 15 units arrived.

Here is the current status of the board.

@AndyPF, I believe I need a few hours to finish first attempt to route. I would love to have a second pair of eyes reviewing it...

Por sdsnatcher73

Enlighted (4322)

21-08-2022, 07:36

Seeing that chips are available in bulk only makes me think we should consider some strategy. Obviously there is a sizable community in Brazil but there are much bigger communities in Europe and Japan. I think it would be best if these were produced “locally”. Maybe the sellers would consider selling 240 chips and splitting them before shipping? Then we could send them to producers in Brazil, Europe and Japan.

That would help keeping final cost (especially shipping to end user) down. Allowing for easier access for everyone and getting enough sales to justify the large investment in these chips.

Por crisag

Expert (122)

21-08-2022, 21:53

I'll check with the sellers. I doubt they will do that as they are big distributors and don't see any value taking care of small sales. I said, I had to beg to get 15 as a trial.

Back to the project we had a lot of progress this weekend. I finished rev1 routing and next step is to validate the circuit and perform corrections to the board before first trial batch. I intend to do that after work during this week and next weekend, lets see.

As you can see in the following images I came back with the holes on the PCB and reduced the size of the 14.3 oscillator to DIP4 as I have a bunch laying around here.

@sdsnatcher I saw your comment with respect to superimpose. Do you happen to have a sample circuit to support that? I didn't see the reference circuit for that feature on the V9990 documentation.

Here are the latest images of the board. Everything is updated on GitHub in case you want to take a look and propose changes/improvements.

Por sdsnatcher73

Enlighted (4322)

22-08-2022, 06:02

Quote:

I'll check with the sellers. I doubt they will do that as they are big distributors and don't see any value taking care of small sales. I said, I had to beg to get 15 as a trial.

I guess the next best option is someone in Japan buying them and distributing them to Brazil and Europe. That way you prevent excessive shipping around the world as well as double taxes (I mean paying shipping and taxes first to get the chips to Brazil and then again if you ship them to Europe).

Por gdx

Enlighted (6449)

22-08-2022, 13:00

To sell in Japan, you might have to put back the Kanjis that were removed.